US2695299A - Mercaptobenzothiazoles - Google Patents

Description

2,695,299 Patented Nov. 23, 1954 fiice MERCAPTOBENZOTHIAZOLES Joachim Dazzi, Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application June 23, 1950, Serial No. 170,049

3 Claims. (Cl. 260306) The present invention relates to new derivatives of 2- mercaptobenzothiazole and to methods of preparing the same.

The invention provides products having the general formula in which n is an integer of from I to 30 and R is a memberof the group consisting of hydrogen and saturated hydrocarbon residues of from 1 to 29 carbon atoms.

One class of compounds having the above general formula includes members having the general structure in which R is a member of the group consisting of hydrogen and saturated hydrocarbon residues of from 1 to 29 carbon atoms. This class of compounds includes esters of saturated, hydrocarbon monocarboxylic acids of from 1 to 30 carbon atoms and 2(2-benzothiazylrnercapto)- ethanol. The latter compound is readily obtainable by reaction of one mole of Z-mercaptobenzothiazole with one mole of ethylene oxide, ethylene glycol or ethylene chlorohydrin.

Another class of compounds includes esters of the saturated, hydrocarbon monocarboxylic acids and products obtainable by reaction of one mole of mercaptobenzothiazole with more than one mole of ethylene oxide. This class has the general formula in which n is an integer of from 1 to 29 and R is as herein defined. Condensation products of one mole of 2- mercaptobenzothiazole with from 5 to 30 moles of ethylene oxide are described in the Gluesenkamp U. S. Patent No. 2,498,617, which is assigned to the same assignee as is the present case.

Accordingly, the present invention relates generally to esters of saturated, hydrocarbon monocarboxylic compounds of from 1 to 30 carbon atoms and a member of the group consisting of 2-(Z-benzothiozylmercapto)ethanol and polyglycols obtained by reacting mercaptobenzothiazole with more than one mole of ethylene oxide, such esters being obtained substantially according to the scheme in which is an integer of from 1 to 30, R is a hydrocarbon residue of from 1 to 29 carbon atoms and X is a member of the group consisting of hydroxy, OCOR, chlorine and bromine. As carboxylic components there may be employed, for example, such aliphatic carboxy compounds as formic acid, acetyl bromide, acetic anhydride, propionyl chloride, butyric anhydride, valeric acid, 2-ethylhexoic acid, lauroyl chloride, myristoyl bromide, behenic acid, cerotic acid and melissic acid; such aromatic compounds as benzoyl chloride, 3-biphenyl carboxylic acid and Z-naphtoic acid; such alicyclic compounds as cyclohexanecarboxylic acid and Z-methylcyclohexanecarboxylic acid; and such aralkyl compounds as 2- toluic acid, u-toluic acid, and hydrocinnamic acid.

Esterification of benzothiazylmercaptoethanol or of the higher ratio mercaptobenzothiazole-ethylene oxide condensation products with the above carboxylic compounds takes place readily at ordinary, increased or decreased temperatures depending upon the nature of the reactants. When using the free acids, some esterification occurs upon contacting the two reactants at ordinary temperatures, but optimum yields of the present esters are obtained by heating a mixture of the mercapto compound and the acid, preferably at refluxing .temperature and in the presence of an esterifying catalyst. As esterifying catalysts suitable for the present purpose may be mentioned acidic or basic materials such as sulfuric acid, phosphoric acid, p-toluenesulfonic acid, sodium methoxide, etc.

When working with acid halides optimum yields areobtained when operating at decreased temperatures, i. e., at temperatures of, say, from minus 10 C. to 10 C. With these highly reactive esterifying agents, the use of a catalyst is unnecessary and often detrimental to smooth condensation.

Inasmuch as the esterification reaction involves the con-, densation of one mole of the hydroxy thiazole compound with one mole of the acid, stoichiometric proportions of the reactants are advantageously employed. However, since any excess of either the hydroxy compound or the acid may be readily recovered from the final product, the quantity of reactants employed in the initial reaction is immaterial. It is preferred, however, to use an excess of the acid compound in order to minimize incomplete esterification.

The present products are stable, somewhat high-boiling materials which range from viscous liquids to waxy or crystalline solids. They may be employed for a variety of technical uses, i. e., as plasticizers for synthetic resins and plastics, and as intermediates in the production of moisture-proofing agents, biological toxicants, surfaceactive agents, etc.

Advantageously employed as plasticizers, particularly for vinyl chloride polymers, i. e., polyvinyl chloride and copolymers of vinyl chloride with unsaturated monomers, are esters having the general structure more may be mentioned the 2-(benzothiazylmercapto)- ethyl esters of valeric acid, n-hexoic acid, pelargonic acid, laurie acid, 2-napthioic acid, hydrocinnamic acid and cyclohexanecarboxylic acid and the esters of these acids with Z-mercaptobenzothiazole-ethylene oxide condensation products in which the molar ratio of mercapto compound to ethylene oxide is 1:2 and 1:3.

I have found that esters of 2-(benzothiazylmercapto)- ethanol of of Z-mercaptobenzothiazole-ethylene oxide condensation products having the formula shown above are of outstanding value as plasticizers for polyvinyl chloride and for copolymers of at least per cent by weight of vinyl chloride and up to 30 per cent by weight of an unsaturated monomer copolymerized therewith, for example vinyl acetate, vinylidene chloride, etc. These esters not only soften vinyl chloride polymers but also impart a high degree of low temperature flexibility, very good temperature stability and great mechanical strength to these polymers. They are compatible with vinyl chloride polymers and show no exudation of plasticizer even at plasticizer content of up to 50 per cent. Although the quantity of plasticizer will depend upon the particular polymer to be plasticized and upon its molecular weight, it is generally found that compositions having from per cent to 50 per cent by weight of plasticizer will, in most cases, be satisfactory for general utility. The good flexibility of the plasticized compositions increases with increasing plasticizer concentration.

In evaluating plasticizer efficiency use is made of the following empirical testing procedures:

Compatibility.--Visual inspection of the plasticized composition is employed, incompatibility of the plasticizer with the polymer being demonstrated by cloudiness and exudation of the plasticizer.

Low temperature flexibility.-Low temperature flexibility is one of the most important properties of elastomeric vinyl compositions. While many plasticizers will produce flexible compositions at room temperature the flexibility of these compositions at low temperatures may vary considerably, i. e., plasticized polyvinyl chloride compositions that are flexible at room temperature often become very brittle and useless at low temperatures. Low temperature flexibility tests herein employed are according to the Clash-Berg method. This method determines the torsional flexibility of a plastic at various temperatures. The temperature at which the vinyl composition exhibits an arbitrarily established minimum flexibility is defined as the Low Temperature Flexibility of the composition. This value may also be defined as the lower temperature limit of the plasticized compositions usefulness as on elastomer.

Water resistance.The amount of leaching that takes place when the plasticized composition is immersed in distilled water for 24 hours is determined.

The invention is further illustrated, but not limited, by the following examples:

Example I To a solution of 211.4 g. (1 mole) of 2-(2-benzothiazylmercapto)ethanol (prepared by the reaction of mercaptobenzothiazole with ethylene chlorohydrin) in an excess of toulene there Was added 173 g. (1.2 moles) of 2-ethylhexoic acid and 5 g. of p-toluenesulfonic acid as a catalyst. The resulting mixture was then refluxed for a time of 8 hours, during which time water was removed from the reaction zone as it was formed. Removal of the solvent and excess 2-ethylhexoic acid from the resulting reaction product gave substantially pure 2-(2-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P. 201 C. to 208 C./0.7 mm. of mercury.

Example 2 To a solution of 110.6 g. (0.5 mole) of 2-(2-benzothiazylmercapto)ethanol (prepared by reaction of henzothiazole with ethylene oxide in 245.4 g. of xylene) there was added 33.9 g. of dry pyridine and 50 ml. of ether. The resulting mixture was then cooled to a temperature of minus 5 C. to 0 C. and during a period of 42 minutes there was added to the cooled mixture 85.5 g. (0.525 mole) of 2-ethylhexoyl chloride. The whole was then stirred for 3.5 hours at a temperature of from minus 2 C. to 3 C., diluted with water, and washed neutral. Removal of the solvents by distillation at up to 100 C./l mm. pressure yielded 128 g. of crude 2-(2-benzothiazylmercapto)ethyl 2 ethylhexoate, n =1.5608. Since the crude product was found to have an acid value of 9.67 percent (indicating the presence of unreacted acid) it was again submitted to esterification by refluxing it for a period of 3 hours with 0.5 mole of 2-ethylhexoic acid in the presence of a small amount of p-toluenesulfonic acid as esterifying catalyst and an excess of toluene as diluent. During this time 1.5 ml. of water was collected, showing further esterification. At the end of that time the product was fractionally distilled to yield the substantially pure 2-(Z-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P. 200 C. to 210 C. at 0.7 mm., n =1.5625.

Example 3 Into a 250 ml. three-necked flask fitted with an agitator, thermometer and dropping funnel was placed 90 g. (0.1 mole) of a 23.5 percent solution of 2-(2-benzothiazylmercapto)ethanol in p-xylene and 9 g. (0.11 mole) of pyridine. The mixture was cooled in a saltice bath while 24.7 g. (0.1 mole) of myristoyl chloride was added over a period of one hour. The flask contents were stirred an additional hour while in the ice bath and then for another 80 minutes at room temperature. The reaction mixture was washed two times with water, once with a dilute sodium bicarbonate solution, three more times with water, dried over calcium chloride, filtered and distilled under reduced pressure to a pot temperature of 80 C./ 3 mm. There was thus obtained 39 g. of 2-(2-benzothiazylmercapto)ethyl myristate as residue.

Proceeding substantially as in the above examples 2- (2-benzothiazylmercapto)ethanol may be similarly reacted with other saturated, unsubstituted monocarboxylic acids of from 1 to 30 carbon atoms. Thus, instead of the carboxylic acids employed in the above examples there may be used, e. g., acetic acid, butyric acid, n-caproic acid, capric acid, stearic acid, cyclohexanecarboxylic acid, a-toluic acid, benzoic acid, 4-phenylbenzoic acid, etc. to yield the 2-(Z-benzothiazylmercapto)ethyl esters thereof. Also, instead of 2-(Z-benzothiazylmercapto)ethanol there may be employed reaction products of one mole of 2- mercaptobenzothiazole with more than one mole of ethylene oxide, i. e., condensation products prepared from one mole of Z-mercaptobenzothiazole and from 2 to 30 moles of ethylene oxide.

Example 4 Sixty parts of polyvinyl chloride and 40 parts by weight of the 2-(2-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P. 200 to 210 C. of Example 2 are mixed on a rolling mill to a homogeneous blend. During the milling there was observed substantially no fuming and discoloration. A molded sheet of the mixture was clear and transparent and substantially colorless. Testing of the molded sheet for low temperature flexibility, according to the testing procedure described above, gave a value of minus 26 C., which value denotes extremely good low temperature properties. Tests of the water-resistance properties of the plasticized material employing the test procedure described above showed a solids-loss of only 0.2 percent.

Instead of the 2 (2 benzothiazylmercapto)ethyl 2 ethylhexoate employed in the above example there may be advantageously employed as plasticizers for polyvinyl chloride and for copolymers of vinyl chloride other esters having the general structure in which n is an integer of from 1 to 3 and R is a member of the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals of from 4 to 12 carbon atoms, e. g., the 2-(benzothiazylmercapto)ethyl esters of butyric acid, capric acid, lauric acid, 4-toluic acid, hydrocinnamic acid or cyclohexanecarboxylic acid. Also, instead of using the 2-(benzothiazylmercapto)ethyl esters of these acids there may be employed esters of the above acids and the condensation products of one mole of 2-mercaptobenzothiazole with from 2 to 3 moles of ethylene oxide.

While the above example particularly illustrates compositions in which the ratio of plasticizer to polymer content is 40:60, this ratio being employed in order to get comparable efliciencies, the content of ester to polyvinyl chloride may be widely varied, depending upon the properties desired in the final product. For many purposes a plasticizer content of, say, from only 10 percent to 20 percent is preferred. The above esters are compatible with polyvinyl chloride over wide ranges of concentrations, up to 50 percent of esters based on the total weight of thepla'sticized composition yielding desirable products.

Although the invention has been described particularly with reference to the useof the present esters as plasticizers for polyvinyl chloride, these esters are advantageously employed also as plasticizers for copolymers of vinyl chloride, for example the copolymers of vinyl chloride with vinyl acetate or'vinylidene chloride, etc.

Preferably such copolymers have a high vinyl chloridecontent, i. e., a vinyl chloride content of at least 70 per- 6 cent by weight of vinyl chloride and up to 30 percent by in which n is an integer of from 1 to 3 and R is an alkyl Weight of the copolymerizable monomer. radical of from 4 to 14 carbon atoms.

The plasticized polyvinyl halide compositions of the 2. 2-(2-benzothiazylmercapto)ethyl 2-ethy1hexoate. present invention have good thermal stability; however, 3. 2-(Z-benzothiazylmercapto)ethyl myristate. for many purposes it may be advantageous to use known 5 stabilizers in the plasticized compositions. The esters References Cited 111 the file 0f thlS Patent are of general utility in softening vinyl chloride polymers. UNITED STATES PATENTS They may be used as the only plasticizing component in a compounded vinyl chloride polymer or they may be Number Name Date used in conjunction with other plasticizers. 10 75,0 le a der 00L 3, 1939 WhatIclaimis: 2,175,049 Alexander Oct. 3, 1939 1. Compounds having the general formula 1 l f r A g- 1 1 40 2,280,792 Bruson Apr. 28, 1942 2,323,037 Harman June 29, 1943 g 15 2,407,138 Clifford et a1 Sept. 3, 1946 S(CHzOHaO),,OGR 2,498,617 Gluesenkamp Feb. 21, 1950

Claims (1)

1. COMPOUNDS HAVING THE GENERAL FORMULA