Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/04—Preparation of derivatives of isocyanic acid from or via carbamates or carbamoyl halides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/18—Separation; Purification; Stabilisation; Use of additives
  • C07C263/20—Separation; Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C265/00—Derivatives of isocyanic acid
  • C07C265/02—Derivatives of isocyanic acid having isocyanate groups bound to acyclic carbon atoms
  • C07C265/04—Derivatives of isocyanic acid having isocyanate groups bound to acyclic carbon atoms of a saturated carbon skeleton

Definitions

• the present invention relates to a process for producing methyl isocyanate.
• alkyl isocyanates by the pyrolysis of alkyl or aryl carbamates is well known (see for example Ann 562 205 (1949) and Methoden der Orgeneschem Chemie, Vol. 8, 126 (1952)).
• the conventional processes involve decomposing an alkyl or aryl carbamate at elevated temperatures to produce the isocyanate together with either an alcohol or phenol as a by-product, as illustrated in the following equation:
• R and R 1 are alkyl or aryl.
• phenyl N-alkylcarbamates also known as phenyl N-alkyl urethanes
• the thermal decomposition of phenyl N-alkylcarbamates must be conducted in the presence of an added amount of phenol or using a reaction mixture having a molar ratio of phenol to phenyl N-methyl urethane not lower than 1:1 throughout the thermal decomposition period.
• phenyl N-alkylcarbamates also known as phenyl N-alkyl urethanes
• the use of high-boiling inert solvent for the thermal decomposition of aryl N-alkylcarbamates is disclosed in U.S. Patent 3,919,278 issued on November 11, 1975 to Rudolph Rosenthal.
• isocyanates are produced by thermally decomposing esters of carbamic acids (i.e., urethanes or alkyl carbamates) dissolved in a suitable inert solvent and the corresponding isocyanate and alcohol are recovered separately.
• carbamic acids i.e., urethanes or alkyl carbamates
• alk lisocyanates are prepared by reacting a phenol or substituted phenol and phosgene in dichloromethane with aqueous caustic solution to produce a chloroformate derivative.
• the chloroformate is then reacted with aqueous alkylamine to yield an N-alkylcarbamate compound which, after the solvent is stripped, is pyrolized to yield the alkyl isocyanate.
• U.S Patent 4,195,031 issued
• March 25, 1980 discloses a process for the continuous production of monoisocyanate.
• the patent discloses the use of a packed column in the process for decomposing aryl methylcarbamate in the generation of methyl isocyanate.
• the process however utilizes a high-boiling organic solvent to aid the decomposition process.
• the present invention is particularly suitable for the production of methyl isocyanate.
• methyl isocyanate is an important carbamoylating agent for the manufacture of a variety of methyl carbamate pesticides.
• MIC can be generated easily in high yields (greater than 85%) by thermal decomposition of phenyl N-methylcarbamate, which is a relatively non-toxic compound.
• MIC can be produced on-site as needed thus eliminating the handling and shipping of this highly toxic material.
• the present invention provides a process for the preparation of methyl isocyanate which comprises heating a phenyl N-methylcarbamate compound in a decomposition zone said phenyl N-methylcarbamate being represented by the formula:
• n is an integer of 0 to 5 and each R is individually an alkyl of 1 to 5 carbon atoms, to form methyl isocyanate and a phenol corresponding to the phenolic moiety of the said phenyl N-methylcarbamate as a by-product and simultaneously or immediately thereafter rapidly separating said methyl isocyanate from said phenol to inhibit reformation of said phenyl N-methylcarbamate compounds.
• phenolic moieties in the above formula are 4-methylphenyl, 2-isopropylphenyl, 2-(l-methylpropyl) ⁇ henyl, 3-ethylphenyl and the like.
• the preferred starting compound is phenyl N-methylcarbamate which decomposes to form phenol and methyl isocyanate.
• Fig. 1 is diagram of the apparatus employed for the cracking operation. DESCRIPTION OF THE PREFERRED EMBODIMENTS According to an embodiment of the process of the present invention, the decomposition of phenyl N-methylcarbamate is conducted in the absence of any inert solvent or any substance which adversely affects the decomposition or the recovery of reaction products.
• the temperature and pressure conditions are such as to remove by vaporization, from the reaction environment both the phenol and the methyl isocyanate as they are being formed.
• An important aspect of the present invention is that the vaporized phenol and methyl isocyanate must be rapidly separated in order to inhibit formation of the starting material.
• a sufficient residence time must be also provided for the decomposition of the phenyl N-methylcarbamate. It has been found that the use of a packed column directly above the reaction vessel will provide the necessary time for the decomposition reaction.
• the decomposition process can be carried out at atmospheric, sub-atmospheric, and super-atmospheric pressure. However, in general, slightly super-atmospheric pressures are preferred in order to provide a forward flow of the vaporized products.
• the decomposition reaction can be conducted at a temperature range of from about 170°C to about 270°C, preferably at a temperature range of about 190°C to 230°C.
• methyl isocyanate must be rapidly separated from the phenolic by-product so that little or none of the phenol remains in the decomposition zone to react with formed methyl isocyanate.
• FIG. 1 illustrates the equipment useful for conducting the decomposition reaction and rapidly separating the phenol from the methyl isocyanate.
• a reactor vessel 10 preferably of glass construction and which can be equipped with agitation means and as provided by magnetic stirrer 1 .
• the vessel 10 can be provided with temperature indication means such as thermometer 12, and with a gas inlet 16 for introduction of an inert gas such as nitrogen.
• Reactor vessel 10 can be heated by heater 17 which can be any available conventional type heater adapted to heat reactor vessel 10 to the required temperature.
• Reactor vessel 10 is further provided with outlet 18 to which is mounted column 20 which is an insulated column packed with Raschig rings. Column 20 is wired for electrical heating (not shown) for maintaining temperatures in the column at the required ranges.
• Column 20 is topped with a distillation device 22 including a condenser 24 equipped with cooling means for condensing phenol which collects in collector 26 and passes through line 28 into phenol receiver 30. Vapors containing methyl isocyanate passes from condenser 24 through line 32 into cold trap 34 which is equipped with cooling means (not shown) for collecting methyl isocyanate which is directed through line 36 into receiver 38.
• a quantity of a phenyl-N-methylcarbamate compound is charged to reactor 10 and heated to temperatures of about 170°C to about 270°C under atmospheric pressure accompanied with stirring by stirrer 14 and a nitrogen gas charge which is introduced through line 16.
• vapors of phenol by-product and methyl isocyanate are evolved which must be rapidly separated and recovered.
• the evolved vapors pass through outlet 18 through column 20 which is maintained at 90°C to about 230°C, and through distillation device 22 containing condenser 24 which is maintained at a temperature of about 60°C to about 70°C. At these temperatures the phenol is condensed and is collected in collector 26 thereafter passing through line 28 into phenol receiver 30.
• the vapor stream containing methyl isocyanate leaves condenser 24 through line and enters a second condenser or cold trap 34 which is maintained at temperatures sufficient to condense the methyl isocyanate from the vapor stream. Generally temperatures of about -30°C to about 0°C are suitable for this purpose. Methyl isocyanate leaves cold trap 34 through line 36 and is collected in receiver 38.
• the process of the present invention after a period of about 2-4 hours, excellent recovery of both methyl isocyanate and phenol is achieved.
• the process can be carried out either as a batch process or as a.continuous process by continuously feeding of molten phenyl N-methylcarbamate into the reaction zone while maintaining decomposition conditions.
• the following examples will further illustrate the invention.
• Example I A quantity of phenyl N-methylcarbamate (151.3 g, 99% pure) was charged to a 500 ml glass vessel fitted with a thermostat-controlled heating mantle. The flask was equipped with a magnet stirrer, thermometer, nitrogen inlet and topped with an 18 inch (I.D. 1") insulated column packed with Raschig rings. The column was wired for electrical heating and was kept at 90-170°C during the decomposition reaction. The column was topped by a distillation device with a condenser kept at 60°C for collecting phenol; at the top of the condenser was a cold trap (0°C) for the collection of methyl isocyanate.
• I.D. 1 18 inch
• the phenyl N-methylcarbamate in the reaction flask was initially heated to about 220°C and was being stirred.
• the vaporized methyl isocyanate and phenol were removed separately and simultaneously as they were formed while kept at 200-217°C.
• the decomposition reaction was maintained in this manner until no more methyl isocyanate and phenol were distilled over, and a flask temperature of 260°C was reached.
• a total of 49.6 g of methyl isocyanate was collected in the cold trap.
• the phenol receiver recovered 71.8 g of material consisting of 95.9 percent of phenol and 4.1 percent of phenyl N-methylcarbamate.
• the residue left in the reaction flask was 15.1 g containing 82.1 percent of phenol, 13.8 percent of phenyl N-methylcarbamate, and 4.1 percent of unknown materials.
• the yield of methyl isocyanate was 88 percent based on the amount of material recovered.
• Example II The apparatus and procedure were as illustrated and described in U.S. Patent 4,514,339.
• a mixture of 56.48 g (0.37 mole) of phenyl N-methylcarbamate and 35.17 g (0.37 mole) of phenol was charged to a glass flask, which was fitted with a thermostat-controlled heating mantle and was equipped with a magnetic stirrer, thermometer, and a nitrogen inlet-tube.
• the flask was topped by a distillation device with a condenser maintained at 70°C for the collection of phenol and a subsequent cold trap (0°C) for collecting the methyl isocyanate.
• the mixture in the reaction flask was heated to boiling at 198-215°C under a nitrogen atmosphere and was being stirred.
• Example III A quantity of 2-(l-methylpropyl)phenyl N-methylcarbamate (171.7 g, 0.82 mole) was charged to the same equipment as described in Example I. During the thermal decomposition period, the column was kept at 90-222°C while the reaction kettle was kept at 210°C to 270°C.

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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1987
  • 1987-03-18 GR GR870442A patent/GR870442B/el unknown
  • 1987-03-18 IL IL81939A patent/IL81939A0/xx unknown
  • 1987-03-20 HU HU872424A patent/HUT47532A/hu unknown
  • 1987-03-20 EP EP87902898A patent/EP0275263A1/en not_active Withdrawn
  • 1987-03-20 JP JP62502269A patent/JPS63503063A/ja active Pending
  • 1987-03-20 ZA ZA872075A patent/ZA872075B/xx unknown
  • 1987-03-20 WO PCT/US1987/000537 patent/WO1987005600A1/en not_active Application Discontinuation
  • 1987-03-20 AU AU72345/87A patent/AU7234587A/en not_active Abandoned
  • 1987-03-20 CN CN198787102215A patent/CN87102215A/zh active Pending
  • 1987-03-20 ES ES8700782A patent/ES2003696A6/es not_active Expired
  • 1987-03-20 KR KR1019870701069A patent/KR880701225A/ko not_active Application Discontinuation
  • 1987-03-20 BR BR8707253A patent/BR8707253A/pt unknown
  • 1987-11-20 FI FI875152A patent/FI875152A0/fi not_active Application Discontinuation

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