CA1240156A - Process for preparing finely divided highly reactive magnesium and use thereof - Google Patents

Abstract

Process for Preparing Finely Divided Highly Reactive Magnesium and Use Thereof Abstract of the Disclosure The present invention relates to a pro-cess for preparing a finely divided, highly reactive magnesium from magnesium hydride, magnesium anthracene and/or its derivatives or magnesium butadiene and/or its alkyl or phenyl derivatives, which process is characterized in that the respective magne-sium-containing compound is thermally decom-posed at a pressure from 10-6 to 1 bar the de-composition being carried out in the presence of a co-reactant of a consecutive reaction, or such co-reactant being added only after com-pletion of the precipitation of the magnesium, or in the absence of such co-reactant, the mag-nesium obtained by said decomposition being isolated as a powder, and to the use of the finely divided, highly reactive magnesium for inserting magnesium into poorly reactive C-X bonds, wherein X denotes hetero-atoms such as halogen, oxygen, sulfur, nitro-gen, phosphorus, and the resulting organomagne-sium compound may be used in a consecutive re-action according to a per se known method, and for the reversible preparation of active magne-sium hydride by reaction with molecular hydro-gen at a pressure of from 1 to 2 bar and at a temperature of from 150°C to 250°C.

Description

Process for Preparing Finely Divided Highly Reactive Magnesium and Use Thereof -The invention relates to a process for pre-paring a finely divided, highly reactive magnesium and the use thereof.

Activated forms of metallic magnesium are used to an increasing extent in chemical syntheses, more specifically for Grignard reactions, as redu-cing agents, for dehalogenation reactions and the like. Thereby, most of said reactions can be effected with a substantially higher efficiency than, e.g., by using commercially available magne-sium powder, while other reactions have only become realizable therewith (cf., e.g., Y.-H. ~ai, Synthe-sis 585 (1981); W. Oppolzer in "Current Trends in Organic Synthesis", Ed. H Nozaki, Pergamon Press 1983, p. 131). According to R.D. Rieke, magnesium can be obtained in an active form by reduction of magnesium halides with alkali metals, more particu-larly with potassium, in tetrahydrofuran (THF) (Acc.
Chem. Res. 10, 301 (1977)) or 1,2-dime'thoxyethane, optionally with the addition of naphthalene as an electron transfer agent (Arnold & Kulenovic, Synth.
Commun. 7, 223 (1977); Rieke et al., J. Org. Chem.

- 2 - ~ 2 ~0~56 46 4323 (1981)) These methods have disadvantages in as much as activated magnesium is obtained suspended in THF or 1,2-dimethoxyethane as a mixture with the respective alkali metal halide and mostly also with the alkali metal so that for the preparation of active magnesium by said route equimolar amounts of alkali metal, e.g. metallic potassium, are required.

It is the object of the present invention to provide a process for the preparation of highly active magnesium, which process is free from the aforementioned drawbacks and, in addition, is suit-able for being carried out on a larger scale.

There has been known that an equilibrium exists between metallic magnesium and hydrogen, on the one hand, and magnesium hydride, on the other hand, which equilibrium inherently is temperature-dependent and reversible:

Mg + H2 ~ MgH2, ~H = -74,8 kJ/mol (1) At room temperature and under regular pres-sure, the equilibrium of equation (1) is almost completely on the magnesium hydride side. With in-creasing temperature, the hydrogen partial pressure of magnesium hydride increases and, for example, reaches the values of 1, 2 and 5.5 bar at a tempera-ture of 284C, 310C and 350C, respectively.
However, the hydrogenation of commercially available magnesium in the absence of catalysts as well as the thermal decomposition of the formed magnesium hydride proceed at an extremely low speed _ 3 _ ~240156 even at a temperature of about 400C (cf., e.g., Stander~ Z. f~r physikal. Chem. Neue Folge 104, 229 tl977)). In addition, in the thermal decomposition of the magnesium hydride prepared at a high tempera-ture there is formed a magnesium metal having a low chemical reactivity, so that said route will hardly be suitable as a method for activating magnesium.

According to the European Patent Specifica-tion No. 0 003 564 (to Applicants) a process has become known which allows magnesium to be hydrogen-ated to give magnesium hydride under mild conditions (eOg. at from 20C to 60C and from 1 to 80 bar) by means o~ the homogeneous catalysts as described therein.

Now, surprisingly there has been found that a finely divided, highly reactive magnesium suspend-ed in a solvent or, upon respective work-up, a pyro-phoric magnesium powder having an unexpectedly high chemical reactivity is formed, when said magnesium hydride generated in the presence of a homogeneous catalyst is thermally dehydrogenated. Therefore, a method according to the invention for preparing a highly reactive and very finely divided magnesium comprises the thermal dehydrogenation under reduced pressure of magnesium hydride having been prepared according to a per _ known process.

According to the U.S. Patent SpecificatiGns No. 3,351,646, 3,354,190 and 3,388,179 metallic mag-nesium in THF will undergo an addition reaction to anthracene and other condensed aromatic ring systems and to butadiene and other conjugated dienes to form 12gl0~L56 the corresponding magnesium adducts of said hydro-carbons, magnesium anthracene, magnesium butadiene etc.. In accordance with our findings, the adducts magnesium anthracene . 3 THF, magnesium butadiene .
2 THF etc. are in a temperature-dependent, reversib-le equilibrium with their respective organic consti-tuents and magnesium metal tEqns. 2 and 3, respect-ively), a low temperature favoring the adduct form-ation.

There has now surprisingly been found that a finely divided, highly reactive magnesium suspended in a solvent or, upon respective work-up, a magne-sium powder having an extremely high chemical re-activity is formed, when magnesium anthracene, mag-nesium butadiene and/or adducts of magnesium to other conjugated dienes having the general formula R -CH=CR2-CH=CH-R3, wherein R , R2 and R3 may be same or different and represent H, a linear or branched alkyl group having from 1 to 6 carbon atoms or a phenyl residue, are decomposed to form metallic magnesium upon shifting the equilibria shown by the following equations 2 and 3 from the right to the left by rising the temperature and/or reducing the concentrations of anthracene and THF, or diene and THF, respectively.

.'!g + ~¦ ~ ' i T~ 3 ,~.
R~ (2`
~ RL ~
~!g +h~r 2 T u., ~~4~9~ T"~
R~

- 5 - ~Z4015~

Therefore, another method according to the invention for activating magnesium comprises first reacting a commercially available magnesium in a per se known manner with anthracene, butadiene or a dif-ferent conjugated dienes having the general formula R -CH=CR -CH=CH-R3, wherein R , R and R3 may be same or different and represent H, a linear or branched alkyl group having from 1 to 6 carbon atoms or a phenyl residue, in THF to form magnesium anthracene . 3 THF, magnesium butadiene . 2 THF etc.
(shifting the equilibria according to the equations 2 and 3, respectively, from the left side to the right side) and subsequently producing the activated magnesium by increasing the temperature and/or reducing the concentrations of anthracene and THF or diene and THF etc. (shifting hack the equilibria according to the equations 2 and 3, respectively, from the right side to the left side) in accordance with the instant process.

In a preferred embodiment of the present invention one procedure for activating the magnesium comprises hydrogenating commercially available magnesium according to the process described in the European Patent Specification No. 0 003 564 to form magnesium hydride and subsequently thermally de-hydrogenating the magnesium hydride having been thus produced at a temperature in excess of 300C under atmospheric pressure, and preferably in excess of 250C under reduced pressure. The hydrogen obtained thereby may be conveniently recycled and used for hydrogenating another magnesium batch in accordance with the homogeneously catalytic process according - 6 _ ~ 2 ~Q~56 to the EP-A- 0 003 564, whereby an economic process for preparing activating magnesium from commercially available magnesium has been provided.

In a further preferred embodiment of the present invention a commercially available magnesium is reacted in a per _ known step with anthracene or one of its alkyl or phenyl derivatives according to eguation (2), or with a conjugated diene having the general formula Rl-CH=CR2-CH=CH-R3, wherein R , R
and R3 may be same or different and represent H, a linear or branched alkyl group having from 1 to 6 carbon atoms or a phenyl residue according to equation (3), and the resulting organomagnesium compound is thermolyzed at an elevated temperature in vacuo or at atmospheric pressure.

The preferred range of temperatures for the decomposition of magnesium anthracene . 3 THF or of magnesium adducts to substituted anthracenes in the solid state is between +70C and +170C. In an inert organic solvent the decomposition is effected under atmospheric pressure at a temperature of from +20C to +100C. As the inert organic solvents there may be used aliphatic, cycloaliphatic and aromatic hydrocarbons as well as open-chain alipha-tic ethers such as diethyl ether and dibutyl ether.

The preferred reaction temperature for the decomposition of magnesium butadiene . 2 THF and of magnesium adducts to optionally substituted conjuga-ted dienes, e.g. 1,4-diphenylbutadiene or isoprene, are from +20C to +150C. As a solvent there is used one of the above-mentioned inert organic solvents.

1~40~5~

In the place of magnesium anthracene or magnesium butadiene, respectively, there may also be employed the magnesium adducts to the alkyl or phenyl derivatives thereof, e.g. 1,4-diphenyl buta-diene or isoprene, for the preparation of finely divided, reactive magnesium, while in the place of THF as a solvent there may be used 2-methyltetra-hydrofurane or THF in combination wit~ N,N,N' ,N'-tetramethylethylenediamine (TM~DA) or 1,2-dimethoxy-ethane.

The decomposition of said thermolabile organomagnesium compounds may optionally be accele-rated by means of a catalyst or promoter which, in addition, possibly may positively affect the pro-perties of the active magnesium (particle size, particle shape, (specific) surface area, type and amount of adsorbed materials); organic halogen compounds, e.g. ethylbromide, 1,2-dichloroethane and 1,2-dibromoethane, and magnesium halides may be used as such compounds.

The decomposition of the thermolabile organomagnesium compounds to form highly reactive magnesium optionally may also be accelerated by some physical technique (ultrasonic treatment, light irradiation, mechanical effects).

The formation of active magnesium may be effected in the presence of the materials which are to react with the active magnesium (such as, e.g., organic halogen or phosphorus compounds) or to interact with the active maqnesium (such as, e.g., - 8 - ~ ~015G

inorganic carriers at the surface of which the active magnesium is to be adsorbed). In these cases the active magnesium may be produced at a temperatu-re substantially lower than ~20C, e.g. at -70C or even less, as it is continuously removed from the equilibrium state (equations 2 or 3, respectively) by the direct reaction with the reactants, e.g. the organic halogen or phosphorus compounds.

On the other hand, the materials with which the highly active magnesium powder prepared accord-ing to the invention is intended to react may also be added to the system after the deposition of the active magnesium has been completed. Upon com-pletion of one cycle of the preparation of the active magnesium, the recovered organic components anthracene, butadiene, THF etc. may be employed to activate another magnesium batch, which process may optionally be operated in a circulation system.

The active magnesium obtainable by the process according to the invention is distinguished by having a particularly high (specific) surface area; thus, e.g., the specific surface area of the magnesium as produced by the thermal decomposition of magnesium anthracene . 3 THF under vacuum is 62 mZ/g.

The high chemical reactivity, as compared to that of commercially available magnesium powder, of the magnesium obtainable by the present process, is evident from, inter alia, that it can be inserted in poorly reactive C-X bonds wherein X denotes hetero atoms such as halogen, oxygen, sulfur, nitrogen, phosphorus and the like.

~.240~5~
g Thus, the active magnesium obtained by the thermolysis of the magnesium hydride prepared in the homogeneous catalytic reaction does already react in THF under mild conditions with aryl chlorides, which are believed to be particularly non-reactive in the Grignard reaction, to form the corresponding Grig-nard compounds in high yields. Allyl chlorides can be converted into the Grignard compounds by means of the active magnesium obtained by the process accord-ing to the invention at a temperature as low as -50C, whereby the Wurtz dimerization of the organic radicals which at higher temperatures increasingly interferes with the conventional Grignard reactions can be almost completely suppressed. For the pre-paration of the allyl Grignard compounds, there is preferably employed the variant of the process according to the present invention wherein the high-ly reactive magnesium is produced at a low tempera-ture in the presence of the respective allyl halide.

There has further been known from the lite-rature (and confirmed by own control experiments) that isobutyl chloride does not react nor form orga-nomagnesium compounds with normal magnesium in hydrocarbons (D. B. Malpass et al. in Kirk-Othmer, Encycl. Chem. Techn., Vol. 16, 3rd edition, p. 555).
In the reaction of isobutyl chloride with active magnesium, obtained by thermolysis of magnesium anthracene in toluene or heptane, respectively, iso-butyl magnesiumchloride was obtained in a yield of about 30% (no optimization was attempted in the experiments).

- lo- 1240156 The high reactivity of the active magnesium obtainable by the thermolysis of magnesium hydride prepared in the homogeneous catalytic reaction or of the magnesium anthracene or magnesium diene, re-spectively, is particularly clearly demonstrated by its cleavage reaction with THF with inserting the metal into a carbon-oxygen bond to form l-oxa-2-magnesia-cyclohexane.

~ + ~1~* - T

Mg = active magnesium Conventional types of magnesium are consi-dered to be inert to THF; the formation of the 1-oxa-2-magnesia-cyclohexane by cleavage of THF with metallic magnesium so far has only been observed when "Rieke magnesium" (Bickelhaupt et al., Hetero-cycles 7, 237 (1977)) was employed.

The results of several experiments show that l-halogenophospholenium-halides (such as, e.g., 1) can be reduced with active magnesium obtained according to the invention from magnesium hydride produced in the homogeneous catalytic reaction to give the corresponding 3-phospholenes (2) a$ lower reaction temperatures and with substantially higher yields than has been possible by means of the re-ductions using normal magnesium having so far been described (L.D. Quinn et al., Tetr. Lett. 26, 2187 (1965).

12~L015~

,R _ ,R
5~> ~ m ~ F ~>

Cl C~i3 C~
1 R = ~I, CH3 2 The high reactivity of the active magnesium having become accessible by the process according to the present invention is also demonstrated by the fact that it absorbs hydrogen at a temperature in excess of 150C at atmospheric pressure slowly (under a pressure of 2 to 3 bar rapidly) to form magnesium hydride without any need of addin~ an activator such as, e.g., in the EP-A- 0 003 564.
These conditions are the mildest conditions under which magnesium has ever been hydrogenated. Commer-cially available magnesium requires drastic reaction conditions to be applied in order to accomplish the hydrogenation.

The present invention is further illustrated by, while not limited to, the following examples.
All experiments described in the Examples have been carried out under argon as protective gas.

Example 1 A glass vessel containing 32.0 g of magnesi-um hydride prepared according to the EP-A- 0 003 564 using a chromium catalyst (Mg : anthracene : CrC13 =
100:1:1; 60C/20 bar) was heated in an electrically - 12 _ 1 2 40~5 6 heatable autoclave at from 0.2 to 10 mbar to reach a temperature of 350C within 2 hours and then main-tained at said temperature until the hydrogen evolu-tion had ceased. The organic components as contain-ed in the reaction mixture were volatilized in ex-cess of 100C, while the endothermic hydrogen evolu-tion started at a temperature in excess of 250C.
Upon cooling, 28.5 g of a gray pyrophoric magnesium powder were obtained which had the following compo-sition: Mg 94.5, C 1.4, H 1.3, Cl 2.2, Cr 0.5 %.

Grignard compounds made from active magne-sium: To the suspension of 3.05 g (117 mmol) of the thus obtained magnesium powder in 50 ml THF there were dropwise added 100 mmol of the aryl chloride or allyl chloride RCl as set forth in the following Table at the temperature indicated in the Table.
After another 30 minutes (during which the tempe-rature was kept constant in the case of the aryl chlorides and was slowly raised to -10C in the case of the allyl chlorides) there was reacted with the respective electrophile and worked up in the conven-tional manner. The products were identified by comparison of their melting points or boiling points, respectively, IR spectra and H-NMR spectra with data reported in the literature.

~240~56 Table RCl TI~C) Elektrophil Product Yield(%)a) " ClSi~CH3)3 C6H5Si(cH3)3 6?

~ +45 H30 ~ 82 cH2=cHcH2cl -50 C02/H30 CH2=cHcH2cooH 83 CIH3 Cl 3 CH3=ccH2cl -50 " CH2=ccH2cooH 72 a) based on chloride used as the starting material.

Example 2 Reaction of the active magnesium with tetra-hydrofuran to form l-oxa-2-magnesia-cyclohexane: A
suspension of 2.43 g (95 mmol) of the active magne-sium prepared as described in Example 1 in 75 ml THF
was heated to reflux for some days. During this period, samples were taken from the solution at de-fined intervals, hydrolyzed and the yield of 1-oxa-2-magnesia-cyclohexane was evaluated by means of the obtained amount of n-butanol (as determined by gas-chromatography (GC)). Amount of n-butanol found (%
of theory) after reaction time (hours; in brackets):
11.4 (51), 19.6 (99) and 25.4 % (243).

~L2~

In two parallel experiments, suspensions of 2.43 g (95 mmol) of the active magnesium in 75 ml THF were heated to reflux for 8 days, the excess of metal was removed by filtration, and to the filtrate there were added dropwise with stirring 50 mmol tri-methylsilyl chloride or benzoylchloride, respective-ly, at -78C.

In the case of the silylation, the reaction mixture was then heated to reflux for 16 hours and thereafter the THF was evaporated under vacuum (14 mbar); the residue was extracted with pentane, the extract was concentrated under vacuum (14 mbar), and the remaining liquid was distilled at 83C to 85C/14 mbar. There were obtained 3.92 g of 4-tri-methylsilyl-butoxytrimethylsilane (Speier, J. Am.
Chem. Soc. 74, 1003 (1952)) (18% based on Mg), which was identified by its H-NMR-spectrum (400 MHz, in CDC13t: ~ (ppm) = -0.05 (s, 9H), 0.08 (s, 9H~, 0.47 (m, 2H), 1.32 (m, 2H),1.52 (m, 2H) u. 3.55 (t, 2H).

In the case of the benzoylation, the react-ion mixture was heated to reflux for 30 minutes; to the residue obtained after evaporation under 14 mbar at room temperature there was added ice water, and the mixture was extracted with ether. The ether extract was evaporated under vacuum at room tempera-ture, and the remaining oil was distilled at 80 to 85C/10 5 bar. There were obtained 3.95 g of 4-ben-zoylbutylbenzoate (Tsuzumi et al. Jap. Pat. 77, 102, 204; Chem. Abstr. 88, 50515 (1978)) (14 ~ based on Mg.), which was identified by its IR and H-NMR
spectra: IR spectrum (film): 1733 and 1695 cm ~4Q~5~:i (~ C O)i 1H-NMR-Spektrum (80 MHz, in CDCl3): S (ppm) = 1.88 (m, 4H), 3.02 (m, 2H), 4.33 (m, 2H), 7.2-7.7 (m, 6H) u. 7.75-8.2 (m, 4H).

Example 3 2.43 g (0.10 mol) of the commercially avail-able magnesium powder having a maximum particle dia-meter of 0.3 mm (50 mesh) were suspended in 0.6 1 of absolute THF, and 32.2 g (0.18 mol) of anthracene and 0.06 ml of ethyl bromide were added to the sus-pension. After 1 hour of stirring at room tempera-ture the orange precipitate of magnesium anthracene began to deposit. Stirring of the suspension was continued for another 48 hours; after filtration the filtercake was washed three times with 50 ml of THF
each and dried under high vacuum. There were obtained 36.2 g of magnesium anthracene . 3 THF
(86.5%) as an orange microcrystalline powder.

A sample of 10.20 g (24 mmol) of magnesium anthracene . 3 THF was first heated under high vacuum at 100C for 1 hour, in the course of which mainly THF was split off and condensed in a receiver cooled with liquid nitrogen. Then the temperature was increased to 150C during 4 hours, in the course of which the removal and sublimation of the anthra-cene occurred. Upon completion of the thermolysis, there were found 4.40 g (83%) of THF (GC analysis) in the receiver cooled with liquid nitrogen and re-covered as sublimate 3.57 g (82%) of anthracene which was identified by its m.p. of 216C and by GC
analysis. As the residue of the thermolysis there - 16 _ 124~S~

remained 0.52 g (88 ~) of a highly reactive black pyrophoric magnesium powder having the following composition (according to elementary analysis): Mg 93.6, C 5.3 and H 0.9 %.

The specific surface area of the magnesium powder (determined according to the BET method, N2 as the adsorption gas) was 62.3 m2/g.

0,42 g of the thus obtained active magnesium in a H2 atmosphere under normal pressure at a tempe-rature of 240C absorbed 318 ml of H2 in the course of 2 hours and 358 ml of H2 after a total of 19 hours (measured under 1 bar at 20C) to form magne-sium hydride (MgH2). The hydrogen uptake, based on the magnesium content of the sample, was 92%.

Example 4 The experiment was carried out as in Example 2, however using the active magnesium obtained by the thermolysis of magnesium anthracene . 3 THF (Ex-ample 3). The raction of the active magnesium with THF to form l-oxa-2-magnesia-cyclohexane proceeded at a similar rate as in Example 2.

Example 5 2.30 g of isobutyl chloride (24.8 mmol) in 30 ml of toluene were dropwise added with stirring to a suspension of 0.65 g (27 mmol) of the active magnesium prepared according to Example 3 in 100 ml of toluene at room temperature within 45 minutes, ~240~5~

and then the reaction mixture was heated at 70C
with stirring for 2 hours. The suspension was fil-tered, and the filtercake was washed with pentane and dried under vacuum (0.2 mbar), whereafter 1.69 g of a solid were obtained which had the following composition (according to elementary analysis): C
32.2, H 5.4, ~g 26.4 and Cl 35.9%. 0.3883 g of this solid upon protolysis with 2-ethyl-1-hexanol and subsequently with 5N H2SO4 yielded 50.4 ml of a gas (0C/1 bar) having the composition (analysis by mass spectrometry (MS)): isobutane 69.6 and H2 30 4 %.
From the isobutane content of the gas, a yield of isobutylmagnesiumchlorid, based on reacted (see belowj isobutyl chloride of 32.7% is calculated. In the toluene solution there were analyzed (by GC or combined GC and ~S analysis, respectively) 0.44 g (4.8 mol~ of isobutyl chloride, 0.05 g (0.4 mmol) of C8H18- (2 isomers) and a total of 0.21 g (1.4 mmol) o~ C11Hl6-hydrocarbons (6 isomers, products of the Friedel-Crafts reaction).

In a control experiment, commercially avail-able magnesium powder having a maximum particle dia-meter of 0.3 mm (50 mesh) did not display any re-action with isobutyl chloride under the same conditions (toluene; 70C; 2 hours).

Example 6 Using 0.71 g (29.2 mmol) of active magnesium (Example 3) and 3.18 g (34.3 mmol) of isohutyl chlo-ride in 130 ml of heptane, however otherwise in analogy of Example 5, the experiment was carried out and the mixture worked up. After filtration 1.71 g ~L~40~56 of a solid having the composition C 35.2, H 5.8, Mg 23.8 and Cl 35.0 % was obtained. Hydrolysis of 0.3908 g of said solid yielded 30.0 ml of isobutane and 14.0 ml of H2 (20C/l bar). The yield of iso-butylmagnesium chloride, based on reacted (see below) isobutyl chloride was 31.6%. In the heptane solution there were found 1.50 g (16.2 mmol) of iso-butyl chloride, 0.06 g (0.5 mmol) of C8H18-hydroca-bons (2 isomers) and 0.7 mmol of diisobutylmagnesium (8.3%)-Example 7 A distillation apparatus e~uipped with adropping funnel was charged with 10.4 g (25 mmol) of the magnesium anthracene . 3 THF prepared as described in Example 3 in 300 ml of toluene; after stirring for 0.5 hours at room temperature the originally orange suspension changed its color to green yellow. The suspension was slowly heated to the boiling point of the mixture, while, beginning at about 70C, the precipitation of a metallic-gray magnesium powder was observed. During 2 hours 538 ml of toluene distilled off while, to the same extent as the solvent distilled, fresh solvent was added dropwise. The precipitated magnesium powder was filtered off, washed with toluene and pentane and dried under vacuum (0.2 mbar). There were ob-tained 0.85 g (71~ of theory) of an active magnesium powder which still contained anthracene. By GC
analysis there were determined 5.23 g of THF (97.4%
of theory) in the toluene removed by distillation, and 4.25 g of anthracene (96~ of theory) in the filtrate.

~2~0~56 , , Example 8 A distillation apparatus equipped with a gas-introducing tube was charged with 14.7 g (66 mmol) of magnesium butadiene . 2 THF (prepared according to Fujita et al. J. Organometal. Chem.
113, 201 (1976)) in 300 ml of *oluene. In the course of warming up the suspension to the boiling temperature while passing argon therethrough, the precipitation of the metallic-gray magnesium powder was observed between 50c and 80c. During 90 minu-tes with the argon stream 173 ml of toluene mixed THF were distilled; the gaseous products formed during the distillation (butadiene) were collected in a cooled trap (-78C) connected to the apparatus.
The precipitated magnesium powder was separated by filtration, washed with toluene and pentane and dried under vacuum (0.2 mbar). There were obtained 1.48 g (92% of theory) of an active magnesium powder comprising 100% of ~g. 6.2 g of THF and 0.2 g of butadiene were found in the distilled toluene, and 1.0 g of THF and 1.4 g of butadiene were found in the condensate collected in the trap.

Example 9 A solution of 2.2 g (20 mmol) of ethyl bromide in 10 ml of toluene was dropwise added to a suspension of 8.4 g ~20 mmol) magnesium anthrace-ne . 3 THF in 50 ml of toluene at 0C with stirring in the course of 30 minutes. The suspension was allowed to warm up to room temperature, and then the precipitated anthracene was separated by filtration.

-- ~24C)~56 20.0 ml (of a total of 60.0 ml) of the solution, upon evaporation of the toluene under vacuum (0.2 mbar) and hydrolysis of the residue with water, yielded 136 ml (measured under 1 bar at 20C) of ethane (according to MS analysis), which correspond to a yield of 85% of ethylmagnesium bromide.

Example 10 Using 10.5 g (25 mmol) of magnesium anthra-cene . 3 THF, 1.9 g (25 mmol) of allyl chloride and 60 ml of THF the experiment was carried out in analogy of Example 9. The yield of allylmagnesium chloride, determined by means of the amount of propene formed upon hydrolysis, was 91%.

Example 11 Using 4.1 g (9.8 ~ol) of magnesium anthra-cene . 3 THF, 0.75 g (9.8 mmol) of allyl chloride and 60 ml of ether the experiment was carried out in analogy of Example 9. The yield of allylmagnesium chloride, determined by means of the amount of propene formed upon hydrolysis, was 98%.

Example 12 Using 8.4 g (20 mmol) of magnesium anthra-cene . 3 THF, 1.5 g (20 mmol) of allyl chloride and 60 ml of toluene the experiment was carried out in analogy of Example 9. The yield of ailylmagnesium chloride, determined by means of the amount of propene formed upon hydrolysis, was 81%.

12~0~56 Example 13 A solution of 1.76 g (23 mmol) of allyl chloride in 40 ml of THF was dropwise added to a suspension of 9.6 g (23 mmol) magnesium anthrace-ne . 3 THF in 100 ml of THF at -70C with stirring in the course of 1 hour, during which period the reaction mixture changed its color into deep blue.
The deep blue suspension was subsequently stirred at -70C for 8 hours. Upon protolysis of the reaction mixture by addition of 5 ml of methanol at -70C, there were recovered 370 ml (measured under 1 bar at 20C) of propene (according to MS analy-sis), which correspond to a yield of 67~ of allyl-magnesium chloride at a reaction temperature of -70C.

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In the process of inserting magnesium into poorly reactive C-X bonds, wherein X denotes a heteroatom selected from the group consisting of halogen, oxygen, sulfur, nitro-gen, phosphorus, and the resulting organomagnesium compound is further reacted in known manner, the improvement which comprises using magnesium produced by thermally decomposing a magnesium-containing compound selected from the group con-sisting of (i) a magnesium anthracene and/or its derivatives pre-pared from magnesium and anthracene and/or its alkyl or phenyl derivatives, (ii) a magnesium butadiene and/or its alkyl or phenyl derivatives prepared from magnesium and a conjugated diene having the general formula R1-CH=CR2-CH=CH-R3, wherein R1, R2 and R3 are the same or different and represent H, a linear or branched alkyl group having from 1 to 6 carbon atoms or a phenyl residue, and (iii) a magnesium hydride-prepared from magnesium and hy-drogen either in the presence of homogenous cat-alysts comprising a halide of a metal of the Sub-groups IV to VII of the Periodic System and an or-ganomagnesium compound or a magnesium hydride and in the presence of a polycyclic aromatic or a tert-iary amine, after hydrogenating magnesium with mag-nesium anthracene or magnesium diene, said thermal decomposition taking place at a pressure from 10-6 to 1 bar and in the absence or presence of an or-ganic apretic solvent, either the decomposition being carried out in the presence of a co-reactant being added only after completion of the precipit-ation of the highly reactive magnesium, or in the absence of such co-reactant, the magnesium obtained by said decomposition being isolated as a highly reactive powder.

2. The process according to claim 1, wherein the de-composition of magnesium hydride is carried out in the ab-sence of a solvent under a pressure of from 0.2 to 10 mbar at a temperature of from 250°C to 300°C.

3. The process according to claim 1, wherein the de-composition of adducts of magnesium to conjugated dienes of the general formula R1-CH=CR2-CH=CH-R3 is carried out in di-ethylether or dibutylether under a pressure of 1 bar and at a temperature of from -100°C to +?150°C.

4. The process according to claim 1, wherein the de-composition of magnesium anthracene . 3 THF or an alkyl or phenyl derivative thereof is carried out in the absence of a solvent under a pressure of from 10-6 to 103 bar at a temp-erature of from +70°C to +170°C.

5. The process according to claim 1, wherein the de-composition of magnesium anthracene . 3 THF or an alkyl or phenyl derivative thereof is carried out in an aliphatic, cy-cloaliphatic or aromatic hydrocarbon or in an open-chain ali-phatic ether under a pressure of 1 bar and at a temperature of from -100°C to +100°C.

6. The process according to claim 1, wherein said ether is selected from the group consisting of diethylether and dibutylether.

7. The process according to claim 1, wherein ethyl bromide, 1,2-dichloroethane, 1,2-dibromoethane and magnesium halides are used as promoters or catalysts, respectively, for the decomposition of said thermolabile magnesium compounds.

8. The process according to claim 1, wherein the de-composition of magnesium hydride is carried out in the absence of a solvent under a pressure of 1 bar at a temp-erature of from 250°C to 350°C.

9. The process according to claim 1, wherein the de-composition of adducts of magnesium to conjugated dienes of the general formula R1-CH=CR2-CH=CH=R3, wherein R1, R2 and R3 are as defined above, is carried out in an aliphatic, cyclo-aliphatic or aromatic hydrocarbon or in an open-chain ali-phatic ether under a pressure of 1 bar and at a temperature of from -100°C to +150°C.

10. In the reversible preparation of active magnesium hydride MgH2 by reaction with molecular hydrogen at a pres-sure of from 1 to 2 bar and at a temperature of from 150°C to 250°C, the improvement which comprises using magnesium pro-duced by thermally decomposing a magnesium-, containing compound selected from the group consisting of (i) a magnesium anthracene and/or its derivatives pre-pared from magnesium and anthracene and/or its alkyl or phenyl derivatives, (ii) a magnesium butadiene and/or its alkyl or phenyl derivatives prepared from magnesium and a conjugated diene having the general formula R1-CH=CR2-CH=CH-R3, wherein R1, R2 and R3 are the same or different and represent H, a linear or branched alkyl group having from 1 to 6 carbon atoms or a phenyl residue, and (iii) a magnesium hydride-prepared from magnesium and hy-drogen either in the presence of homogenous cat-alysts comprising a halide of a metal of the Sub-groups IV to VII of the Periodic System and an or-ganomagnesium compound or a magnesium hydride and in the presence of a polycyclic aromatic or a tert-iary amine, after hydrogenating magnesium with mag-nesium anthracene or magnesium diene, said thermal decomposition taking place at a pressure from 10-6 to 1 bar and in the absence or presence of an or-ganic apretic solvent, either the decomposition being carried out in the presence of a co-reactant being added only after completion of the precipit-ation of the highly reactive magnesium, or in the absence of such co-reactant, the magnesium obtained by said decomposition being isolated as a highly reactive powder.

11. The process according to claim 10, wherein the de-composition of magnesium hydride is carried out in the ab-sence of a solvent under a pressure of from 0.2 to 10 mbar at a temperature of from 250°C to 300°C.

12. The process according to claim 10, wherein the de-composition of adducts of magnesium to conjugated dienes of the general formula R1-CH=CR2-CH=CH-R3 is carried out in di -ethylether or dibutylether under a pressure of 1 bar and at a temperature of from -100°C to +?150°C.

13. The process according to claim 10, wherein the de-composition of magnesium anthracene . 3 THF or an alkyl or phenyl derivative thereof is carried out in the absence of a solvent under a pressure of from 10-6 to 103 bar at a temp-erature of from +70°C to +170°C.

14. The process according to claim 10, wherein the de-composition of magnesium anthracene . 3 THF or an alkyl or phenyl derivative thereof is carried out in an aliphatic, cy-cloaliphatic or aromatic hydrocaron or in an open-chain ali-phatic ether under a pressure of 1 bar and at a temperature of from -100°C to +100°C.

15. The process according to claim 10, wherein said ether is selected from the group consisting of diethylether and dibutylether.

16. The process according to claim 10, wherein ethyl bromide, 1,2-dichloroethane, 1,2-dibromoethane and magnesium halides are used as promoters or catalysts, respectively, for the decomposition of said thermolabile magnesium compounds.

17. The process according to claim 10, wherein the de-composition of magnesium hydride is carried out in the ab-sence of a solvent under a pressure of 1 bar at a temperature of from 250°C to 350°C.

18. The process according to claim 10, wherein the de-composition of adducts of magnesium to conjugated dienes of the general formula R1-CH=CR2-CH=CH-R3, wherein R1, R2 and R3 are as defined above, is carried out in an aliphatic, cyclo-aliphatic or aromatic hydrocarbon or in an open-chain ali-phatic ether under a pressure of 1 bar and at a temperature of from -100°C to +150°C.