GB1595519A - Process for preparing n-(2-mercaptoethyl) amides and2-mercaptoethylamine hydrochlorides - Google Patents

Description

(54) PROCESS FOR PREPARING N-(2-MERCAPTOETHYL) AMIDES AND 2-MERCAPTOETHYLAMINE HYDROCHLORIDES (71) We, THE DOW CHEMICAL COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of Midland, County of Midland, State of Michigan, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- The present invention relates to a process for preparing N - (2 mercaptoethyl)amides and 2 - mercaptoethylamine hydrochlorides.

The chemistry of oxazolines has been reviewed extensively in three major review articles: (1) Wiley et al., Chemical Reviews, Volume 44, 337 (1949); (2) Seeliger et al., Angew. Chem. International Edition, Volume 5, No. 10, 875 (1966); and (3) Frump, Chemical Reviews, 1971, Volume 71, 5483. Such review articles indicate that a wide variety of ring-opening reactions of oxazolines are known but surprisingly few reactions of hydrogen sulfide with oxazolines have ever been considered.

U.S. Patent No. 3,670,046 discloses that certain bisoxazolines react with bismercaptans or hydrogen sulfide to produce polymers. U.S. Patents Nos.

3,630,996, 3,723,451 and 3,746,691 also teach that hydrogen sulfide reacts with certain 2 - alkenyl - 2 - oxazolines to produce the corresponding bis(2 oxazolinylethyl)sulfides. However, none of these references mentions the preparation of N - (2 - mercaptoethyl)alkanamides.

It has now been discovered that N - (2 - mercaptoethyl)amides can be prepared in excellent yield.

Accordingly the present invention provides a process for preparing an N (2 - mercaptoethyl)amide which comprises reacting under anhydrous conditions (a) a 2 - H - 2 - oxazoline or a 2 - alkyl - 2 - oxazoline having the formula

wherein R is a hydrogen atom or an alkyl group containing from I to 18 carbon atoms and each of R1 to R4 are independently a hydrogen atom, a lower alkyl, hydroxy-substituted lower alkyl or phenyl group with (b) hydrogen sulfide.

Such products form a known class of useful compounds having many members, all of which can be hydrolyzed with aqueous HCI to form a 2 mercaptoethylamine hydrochloride which has utility, when neutralized, as an epoxy curing agent, as an acid scavenger and as a pharmaceutical intermediate.

The reactants in the process of the present invention are known classes of reactants. The 2 - H - 2 - oxazolines and 2 - alkyl - 2 - oxazolines correspond to the formula

in which R is a hydrogen atom or an alkyl group containing from I to 18 carbon atoms, and preferably R is a methyl or ethyl group. Each of R, to R4 is independently a hydrogen atom, a lower alkyl (from I to 5 carbon atoms), hydroxysubstituted lower alkyl or phenyl group. Preferably, R, and R2 are each independently a hydrogen atom, a methyl, ethyl or hydroxymethyl group and R3 and R4 are each a hydrogen atom. Most preferably, R, to R4 are each a hydrogen atom.

Examples of suitable such 2 - alkyl - 2 - oxazoline reactants include those of formula I having the values of R and R, to R4 given in Table I.

TABLE I R R, R2 R3 R4 H H H H CH3 H H H H C2H H H H H C,H,s H H H H C"H23 H H H H C"H3s H H H H CH3 C6H5 H H H CsH" C6H5 H H C6H5 C2H5 CH3 H H H CH3 CH3 CH3 H H CsH17 CH2OH CH2OH H H CaHs C4H9 H H C6H5 CH3 H H CH3 CH3 C2H5 H H H C2H5 The 2 - oxazolines used herein are normally prepared by reacting an alkanoic acid with an ethanolamine to form the corresponding acid/amine salt or amide, which in turn is heated in the presence of an aluminum oxide catalyst to form the corresponding 2 - alkyl - 2 - oxazoline product.

The reaction may be conducted neat or in an organic solvent that is inert in the instant process. Suitable such solvents include the lower alkanols containing 1-4 carbon atoms and particularly methanol and combinations of such lower alkanols with conventional hydrocarbon solvents (e.g. benzene, toluene, etc.). It is preferred to conduct the instant process neat or in methanol. It is necessary to conduct the reaction under substantially anhydrous conditions. The 2-oxazolines are susceptible to hydrolysis by water and essentially anhydrous conditions are therefore required to optimize product yield.

The stoichiometry of the reaction requires I mole of hydrogen sulfide per mole of 2 - H - or 2 - alkyl - 2 - oxazoline reactant. More or less than the stoichiometric amount of either reactant can be used. However, it is preferred to use an excess of hydrogen sulfide to effect the completion of the reaction and to maximize the product yield at the expense of by-products, such as bis(alkanamidoethyl) sulfides.

The order of addition or method of blending the reactants is not critical. From a procedural standpoint, however, it is advantageous to add the hydrogen sulfide incrementally to a reaction vessel precharged with the oxazoline reactant, mainly for effectively controlling the reaction temperature.

Substantially any reaction temperature of from about 20C to about 200"C can be used but we normally prefer to conduct the reaction at a temperature of from about 50" to about 150"C. At these temperatures, the reaction may be conducted under autogenous or superatmospheric pressures in conventional pressure equipment. The instant reaction is exothermic and normally will not require additional heat after the reaction is started. Normally, it is advantageous to conduct the reaction in equipment where the temperature can be controlled by cooling.

It has been observed that the reaction rate and product yields are lower when a reaction temperature in lower ranges are used (e.g. from about 20 to about 70 ).

In these instances the product yields can be increased by warming the reaction mixture to the preferred temperature range (e.g. 100"--150"C). This post-heating step appears to cause at least one of the by-products (e.g. a hydroxyethyl thiocarboxamide) to thermally revert to the starting materials and/or rearrange to the desired product.

Example 1 Preparation of N-(2-mercaptoethyl)acetamide A I-liter Parr pressure reactor was charged with 192.2 g of anhydrous methanol and hydrogen sulfide (73.0 g; 2.14 moles; 7 percent excess) and the stirred solution heated to 1000C. 2 - Methyl - 2 - oxazoline (169.3 g; 1.99 moles) was then pumped into the sealed bomb through a check valve at a rate of approximately 2.5 g/minute. The temperature of the stirred solution rose to II 10C during addition and the pressure within the bomb dropped from 320 to 65 psig (22.64.59 kg./cm2). The drop in pressure indicates conversion of H2S to the desired alkanamide. To insure complete conversion, the reactor was heated at this temperature for an additional 4 hpurs. During this post-heating period the bomb pressure remained constant indicating the reaction was essentially complete. The reaction mixture was cooled and volatiles removed therefrom under reduced pressure. Analysis of the remaining pot material by standard iodide/iodate titration (mercaptan functional group analysis) indicated 201.9 g of the desired amide, and 85.1 percent yield based on the oxazoline charged. Distillation under reduced pressure produced a 92.6 percent recovery of a water-white, viscous liquid boiling at 1250C/0.9 mm Hg.

Bis(acetamidoethyl)sulfide was produced as a by-product in amounts which essentially accounted for the remainder of the reactants.

N-(2-mercaptoethyl)propionamide was produced in similarly good yields under essentially the same process conditions.

Example 2 Preparation of N-(2-mercaptoethyl)propionamide 2-Ethyl-2-oxazoline (496.4 g; 5.01 moles) was charged to a l-liter stainless steel Parr reactor, equipped with a stirrer, heating means, and a dip tube designed to introduce H2S below the surface of the liquid oxazoline. The oxazoline was warmed to 700C and hydrogen sulfide (189.5 g, 5.56 moles) was added to the reaction vessel through the dip tube at a rate of 3.7 g per minute. The temperature was maintained at 70"--75"C during the addition of H2S and for an additional 4.3 hours after the addition was complete. The reaction mixture was subsequently heated at 150"C for 5 hours. After this post-heating step, the reaction mixture was cooled to 850C, excess H2S vented to a caustic scrubber, and nitrogen bubbled through the remaining liquid reaction mixture to remove residual H2S. Analysis of the clear, brown liquid product (653.7 g) thus obtained indicated that the desired product, N (2-mercaptoethyl)propionamide, was produced in 86.8 percent of theoretical yield, based on the oxazoline charged. The desired product was recovered from the crude product by use of a falling film still and was thus obtained as a water white liquid containing a minor amount (less than 5 percent) of 2 - ethyl - 2 - thiazoline. The presence of this thiazoline is not a disadvantage since it also hydrolyzes under the conditions set forth below to form the mercaptoethylamine hydrochloride.

Example 3 Preparation of Mercaptoethylamine Hydrochloride An aliquot of the N-(2-mercaptoethyl)acetamide from Example I above (119.2 g; 1.00 mole) and 19.5 percent aqueous HCl (205.6 g; 1.10 mole) were combined in a reaction vessel equipped with a magnetic stirrer and reflux condensor. The reaction mixture was heated to reflux (approximately 107"C) for 4 hours, under a nitrogen blanket. Volatiles were then removed from the reaction mixture under vacuum leaving a viscous, slightly yellow pot liquid which crystallized to a white solid upon cooling. The crystalline material (114.0 g) was identified by its nuclear magnetic resonance and infrared spectra as mercaptoethylamine hydrochloride.

This salt is an item of commerce having several utilities, especially its use as a pharmaceutical intermediate. This salt can also be neutralized with a base (e.g., NaOH) and used as an epoxy curing agent in epoxy resins. Both the mercapto group and amino group are reactive with the epoxy moiety. See "Handbook of Epoxy Resins" by Lee and Neville, McGraw-Hill Book Company (1967). Further, the neutralized salt can be used as an acid scavenger to inhibit acid corrosion.

Other mercaptoethylamines can be similarly used.

WHAT WE CLAIM IS: 1. A process for preparing an N-(2-mercaptoethyl)amide which comprises reacting under anhydrous conditions (a) a 2-H-2-oxazoline or a 2-alkyl-2-oxazoline having the formula

wherein R is a hydrogen atom or an alkyl group containing from I to 18 carbon atoms and each of R, to R4 is independently a hydrogen atom, a lower alkyl, hydroxy-substituted lower alkyl or phenyl group, with (b) hydrogen sulfide.

2. A process as claimed in claim I wherein the reaction is conducted in an inert organic solvent.

3. A process as claimed in claim 2 wherein the solvent is a lower alkanol containing from I to 4 carbon atoms.

4. A process as claimed in claim 3 wherein the organic solvent is methanol.

5. A process as claimed in claim I wherein the process is carried out in the absence of a solvent.

6. A process as claimed in any one of the preceding claims wherein R, and R2 are independently a hydrogen atom, a methyl, ethyl or hydroxymethyl group and R3 and R4 are each a hydrogen atom.

7. A process as claimed in claim 6 wherein R, to R4 are each a hydrogen atom and R is a methyl or ethyl group.

8. A process as claimed in any one of the preceding claims wherein the reaction is conducted at a temperature in the range of from 20 to 2000 C.

9. A process as claimed in claim 8 wherein the reaction is conducted at a temperature in the range of from 50 to 1500C.

10. A process as claimed in any one of claims 1 or 5 to 9 wherein the process is carried out in the absence of a solvent under autogenous or superatmospheric pressure.

II. A process as claimed in any one of the preceding claims wherein a stoichiometric excess of hydrogen sulfide is used.

12. A process as claimed in any one of the preceding claims wherein the hydrogen sulfide is added incrementally to a reaction vessel precharged with the oxazoline reactant.

13. A process as claimed in claim I substantially as hereinbefore described with reference to Example I or Example 2.

14. An N-(2-mercaptoethyl)amide whenever prepared by a process as claimed in any one of the preceding claims.

15. A process as claimed in any one of claims I to 12 including the additional step of hydrolyzing the N - (2 - mercaptoethyl)amide with aqueous hydrochloric acid to thereby form a 2 - mercaptoethylamine hydrochloride.

16. A process as claimed in claim 15 substantially as hereinbefore described with reference to Example 3.

17. A 2 - mercaptoethylamine hydrochloride whenever prepared by a process as claimed in claim 15 or claim 16.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. the neutralized salt can be used as an acid scavenger to inhibit acid corrosion. Other mercaptoethylamines can be similarly used. WHAT WE CLAIM IS:

1. A process for preparing an N-(2-mercaptoethyl)amide which comprises reacting under anhydrous conditions (a) a 2-H-2-oxazoline or a 2-alkyl-2-oxazoline having the formula

wherein R is a hydrogen atom or an alkyl group containing from I to 18 carbon atoms and each of R, to R4 is independently a hydrogen atom, a lower alkyl, hydroxy-substituted lower alkyl or phenyl group, with (b) hydrogen sulfide.

2. A process as claimed in claim I wherein the reaction is conducted in an inert organic solvent.

3. A process as claimed in claim 2 wherein the solvent is a lower alkanol containing from I to 4 carbon atoms.

4. A process as claimed in claim 3 wherein the organic solvent is methanol.

5. A process as claimed in claim I wherein the process is carried out in the absence of a solvent.

6. A process as claimed in any one of the preceding claims wherein R, and R2 are independently a hydrogen atom, a methyl, ethyl or hydroxymethyl group and R3 and R4 are each a hydrogen atom.

7. A process as claimed in claim 6 wherein R, to R4 are each a hydrogen atom and R is a methyl or ethyl group.

8. A process as claimed in any one of the preceding claims wherein the reaction is conducted at a temperature in the range of from 20 to 2000 C.

9. A process as claimed in claim 8 wherein the reaction is conducted at a temperature in the range of from 50 to 1500C.

10. A process as claimed in any one of claims 1 or 5 to 9 wherein the process is carried out in the absence of a solvent under autogenous or superatmospheric pressure.

II. A process as claimed in any one of the preceding claims wherein a stoichiometric excess of hydrogen sulfide is used.

12. A process as claimed in any one of the preceding claims wherein the hydrogen sulfide is added incrementally to a reaction vessel precharged with the oxazoline reactant.

13. A process as claimed in claim I substantially as hereinbefore described with reference to Example I or Example 2.

14. An N-(2-mercaptoethyl)amide whenever prepared by a process as claimed in any one of the preceding claims.

15. A process as claimed in any one of claims I to 12 including the additional step of hydrolyzing the N - (2 - mercaptoethyl)amide with aqueous hydrochloric acid to thereby form a 2 - mercaptoethylamine hydrochloride.

16. A process as claimed in claim 15 substantially as hereinbefore described with reference to Example 3.

17. A 2 - mercaptoethylamine hydrochloride whenever prepared by a process as claimed in claim 15 or claim 16.