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United States Patent (19) 11 Patent Number: 4,740,623 Heather (45) Date of Patent: Apr. 26, 1988 54 METHOD FOR PREPARATION OF BENZYL (57) ABSTRACT MERCAPTAN A method for the preparation of benzyl mercaptain is (75 Inventor: James B. Heather, Hercules, Calif. disclosed which comprises reacting a benzyl halide of 73 Assignee: Stauffer Chemical Company, the formula Westport, Conn. 21 Appl. No.: 9,844 (22 Filed: Jan. 30, 1987 C CH2X 51) Int. Cl* ............................................ CO7C 148/00 52 U.S.C. ...................................................... 568/68 58 Field of Search .......................................... 568/68 wherein X is chlorine or bromine, with an alkali metal hydrosulfide salt, at a temperature and for a sufficient 56 References Cited period of time to cause formation of the benzyl mercap U.S. PATENT DOCUMENTS tan, said reaction being conducted under a hydrogen l,842,414 1/1932 Leaper .................................. 568/68 sulfide atmosphere at a temperature of about 50 C. until 2,456,588 12/1948 Loverde ................................ 568/68 approximately 90% of the starting material is converted 4,082,790 4/1978 Speier .................................... 568/61 to the benzyl mercaptan, then increasing the tempera ture to about 80 C. for the balance of the reaction, the OTHER PUBLICATIONS initial concentration of said hydrosulfide salt in solution W. Hoffman et al, J. Amer. Chem. Soc., vol. 45, p. 1833 being between about 5% and about 30% by weight. (1923). Primary Examiner-Mary E. Ceperley Attorney, Agent, or Firm-Paul R. Martin 6 Claims, No Drawings 4,740,623 1. 2 atmosphere at a temperature of about 50 C. until ap METHOD FOR PREPARATION OF BENZYL proximately 90% of the starting material is converted to MERCAPTAN the benzyl mercaptan, then increasing the temperature to about 80° C. for the balance of the reaction, the initial BACKGROUND OF THE INVENTION 5 concentration of said hydrogen sulfide salt in solution The present invention is related to a method for the being between about 5% and about 30% by weight. preparation of benzyl mercaptan, an intermediate com The preferred benzyl halide for use in the process of pound used in the preparation of S-benzyl thiolcarba the invention is benzyl chloride. Benzyl bromide can be mates, compounds which are known as herbicides. used, but it is more expensive than benzyl chloride. O The preferred alkali metal hydrosulfide salt is the THE PRIOR ART sodium salt. Other salts which can be used include the There are various methods of making benzyl mercap potassium salt. tan which is disclosed in the prior art. One such method, The process as described above results in benzylmer as disclosed in U.S. Pat. No. 4,082,790, comprises react captan of high purity and yield being obtained. ing an aliphatic chloride or bromide with a mixture of 15 There are three elements in the above-described pro H2S and ammonia or an amine at a temperature of 0 to cess which are essential to the practice of this invention. 175' C. under autogenous pressure. This reaction can be The first has to do with the temperature adjustments carried out neat or in the presence of a polar solvent carried out during the period of the reaction. Although such as methanol, isopropanol, or the like. conducting the reaction of lower temperatures leads to Another method disclosed in the prior art (J. A. C. S., 20 reduced levels of benzyl sulfide impurity, the reaction Vol. XLV, 1923, p. 1833, W. S. Hoffman et al.) com prises melting a quantity of crystallized sodium sulfide time becomes excessive. It has been found that main and saturating this with hydrogen sulfide. To this is taining a moderate reaction temperature of about 50 C. added an equal volume of ethyl alcohol and the reaction until the reaction is about 90% complete, then increas mixture is resaturated with the hydrogen sulfide. Fi 25 ing the temperature to about 80 C. for the balance of nally, a quantity of benzyl chloride dissolved in alcohol the reaction, retains to a substantial degree the advan is added. The mixture is allowed to stand in the cold, tage of low benzyl sulfide impurity formation while at with frequent shaking for 4 days, and kept cold to pre the same time bringing about rapid completion of the vent as much as possible the oxidation of the mercaptain reaction. Under these conditions, the level of unreacted to the disulfide and the formation of the monosulfide, benzyl chloride can be reduced to a ow level without which, it is disclosed, takes place readily at high temper appreciably increasing the benzylsulfide level. atures. The effects of the reaction temperature on benzyl A conventional process for making benzyl mercap sulfide by-product content in the benzyl mercaptan tan, as disclosed in U.S. Pat. No. 1,842,414, is to react product are shown in the Table below, wherein a series benzyl chloride with sodium hydrosulfide to form ben 35 of runs are tabulated. In each of these reactions, the zyl mercaptain plus sodium chloride, in accordance with reactants were benzyl chloride and sodium hydrosul the following equation. fide. TABLE I Reaction Temperature Effects Temperature Program Product Composition (gc area %) to 2 A problem which occurs in this reaction, however, is BzCl BzSH Bz2S Initial Completion Final that significant quantities of benzylsulfide are produced 0.2 96.7 .0 50 90% 80 0.2 96.0 1.5 60 90% 80 as a by-product. This reduces the yield of benzyl mer 45 0.1 96.7 1.8 70° 90% 80° captan and increases the need for purification of the 0.2 96.7 1.5 50° 75% 80 product which is produced. It would be advantageous, 0.3 96.2 1.8 50° 60% 80 therefore, to find a process for the production of benzyl *All reactions used 1.3 equivalents of 10% aqueous sodium hydrosulfide and 0.2 mercaptain which minimizes the quantity of benzyl sul equivalents of hydrochloric acid under nitrogen (static). BzCl = benzyl chloride fide by-product formed during the reaction and opti 50 BzSH = benzyl mercaptan mizes the percent yield of the desired benzyl mercaptan Bz.2S = benzylsulfide obtained. This invention is concerned with such a pro CSS. The Table indicates the initial temperature of the DESCRIPTION OF THE INVENTION reaction, as well as the ultimate final temperature. As 55 seen from the Table, the best result in terms of high A process for the preparation of benzyl mercaptan product quality is obtained by conducting the reaction has now been discovered which comprises reacting a at 50° C. to 90% completion, then raising the tempera benzyl halide of the formula ture to 80 C. for the balance of reaction. Under these conditions, approximately 97 weight percent pure CH2X product was obtained upon cooling and phase separa tion. Another critical factor in carrying out the process of the invention is to conduct the reaction in the presence of a hydrogen sulfide atmosphere. The hydrogen sulfide wherein X is chlorine or bromine, with an alkali metal 65 atmosphere should be a static hydrogen sulfide atmo hydrosulfide salt, at a temperature and for a sufficient sphere, which can be maintained by adding a strong period of time to cause formation of benzyl mercaptan, acid (such as HCl) to the reaction solution. This strong said reaction being conducted under a hydrogen sulfide acid results in a hydrogen sulfide gas being generated, 4,740,623 3 4. which is effective in maintaining a hydrogen sulfide sphere, by adding the acid to the slightly larger excess atmosphere over the reaction solution. The atmosphere of sodium hydrosulfide in solution. does not have to be 100% hydrogen sulfide. What is Preferably, about 0.2 equivalents of hydrochloric required is that there be sufficient H2S in the atmo acid and 1.3 equivalents of sodium hydrosulfide per sphere to inhibit the decomposition of sodium hydrosul equivalent of BzCl results in substantially complete fide, thus minimizing the amount of by-products conversion being obtained. formed, described by the following equation: The acid can also serve to adjust the pH of the solu tion to insure that the minimum amount of disodium 2NaSHeNa2S--H2S sulfide is present. Desirably, the pH of the solution Still another critical factor in carrying out the process 10 should be about 8. Commercial sodium hydrosulfide of the invention to obtain maximum yield is to provide preparations conventionally have a pH of about 12. a sufficient quantity of hydrosulfide salt so that it is Thus, if a commercial sodium hydrosulfide is incorpo initially present in solution at approximately 15% con rated into the reaction mixture, the pH should be ad centration by weight. Although reactions conducted at justed downward with the use of the strong acid or by 5% to about 30% concentration give reasonable reac 15 stirring under a hydrogen sulfide atmosphere. tion times, a reaction time of approximately 6 hours can This invention will be more fully understood by ref. be obtained using 15% by weight hydrosulfide salt solu erence to the following examples, which are intended to tions. Higher concentrations of hydrosulfide salt extend be illustrative of the method of the invention, but not the reaction time by a factor of 3 or more. limiting thereof. Over the course of the reaction the quantity of hydro 20 sulfide salt will diminish. However, the starting amount EXAMPLE 1. of the compound should be in the range indicated Preparation of Benzyl Mercaptan above, 5 to 30%. The criticality of the hydrosulfide salt concentration A 500 ml flask with a botton take-off valve was fitted in the solution is demonstrated in accordance with the 25 with a mechanical stirrer, a thermometer, a glass inlet following Table, which represents a series of reactions tube, an addition funnel and a rubber septum.