Process for manufacture of organic esters of strong acids

A method for preparing (R)X.sub.m-p A.sub.p by reacting (R)X.sub.m and MA in N-methylpyrrolidone and recovering the by-product MX as a precipitate wherein: PA0 X is halide; PA0 R contains from 1 to 8 carbon atoms, can be substituted or unsubstituted, and is straight or branched chain alkyl, cycloaliphatic, aralkyl, alkylene, alkenyl, alkenylene, alkynyl or alkynylene with the proviso that X is not attached to a carbon atom having a double bond; PA0 A.sup.- is a monovalent anion soft base selected from the group consisting of halide different from X, SCN.sup.-, SH.sup.-, SO.sub.3 H.sup.-, R.sub.2 PO.sub.4.sup.-, PF.sub.6.sup.-, and [SP(Z) (OR.sup.1).sub.2 ].sup.- wherein R.sup.1 is lower alkyl and z i sulfur or oxygen; PA0 M is an alkali metal or NH.sub.4.sup.+ ; PA0 m is an integer from 1 to 3 with the proviso that m is 1 or 2 when R has one carton; and PA0 P is an integer from 1 to m.

BACKGROUND OF THE INVENTION 
It is known to produce compounds having the formula (R)X.sub.m-p A.sub.p 
(hereinafter Compound III) as defined below by the reaction sequence: 
##STR1## 
wherein: 
X is halide; 
R contains from 1 to 8 carbon atoms, can be substituted or unsubstituted, 
and is straight or branched chain alkyl, cycloaliphatic, aralkyl, 
alkylene, alkenyl, alkenylene, alkynyl or alkynylene with the proviso that 
X is not attached to a carbon atom having a double bond; 
A.sup.- is a monovalent anion soft base selected from the group consisting 
of halide other than X, 3CN.sup.-, SH.sup.-, SO.sub.2 H.sup.-, R.sub.2 
PO.sub.4, R.sub.2 PO.sub.3.sup.-, PF.sub.6.sup.-, and 
[SP(Z)(OR.sup.1).sub.2 ].sup.- wherein R.sup.1 is lower alkyl and Z is 
sulfur or oxygen; 
M is an alkali metal or NH.sub.4.sup.+ ; 
m is an integer from 1 to 3 with the proviso that m is 1 or 2 when R has 
one carbon; and 
p is an integer from 1 to m. 
As used herein, a soft base means an anion of a relatively large size and 
having a diffused charge. See: (1) Pearson, R. G., Survey of Progress in 
Chemistry, 5 (1969, Academic Press); (2) Lowry, T. H., and Richardson, K. 
S., Mechanism and Theory in Organic Chemistry, Harper & Row, New York, NY 
(1976) pp. 165-168; 374-375. Soft bases having the formulas SCN.sup." and 
[SP(Z) (OR.sup.1).sub.2 ].sup.- are disclosed in U.S. Pat. Nos. 
4,087,451, and 3,014,058, respectively. As used herein, lower alkyl means 
an alkyl having from 1 to 4 carbon atoms. 
The R group may be substituted with halide, nitro, cyano, and other 
conventional substituents which do not interfere with the reaction. 
Typical of such compounds is methylene bisthiocyanate which is well-known 
for use limiting the growth and reproduction of microorganisms. It is 
particularly of use in the paper industry to prevent the growth of fungi, 
bacteria, and other microorganisms or enzymes produced by the growth. 
(See, U.S. Pat. No. 3,306,810.) 
Traditionally, this reaction has been carried out in aqueous solvent 
although other solvents, such as cyclic aromatics have been used. (See, 
U.S. Pat. 3,524,871 and British Published Patent Application 2,118,160a.) 
A major problem with the prior art process is that the by-product metal 
halide MX, e.g., sodium bromide, is left in the mother liquor. This is a 
waste material since the compound (R)X.sub.m-p A.sub.p precipitates out 
and is formulated in a separate step from the synthesis. For example, when 
compound III is methylene bisthiocyanate prepared from CH.sub.2 Br.sub.2 
or sodium or ammonium thiocyanate, the mother liquor, after separation of 
the (R)X.sub.m-p A.sub.p contains about 45% of the metal halide, about 3% 
of the reactant MA, and from 0.5-1% of the (R)X.sub.m-p A.sub.p. This is a 
hazardous waste material. The (R)X.sub.m-p A.sub.p which is precipitated 
is then treated in an aqueous dispersion or a nonaqueous solvent, such as, 
dimethyl formamide, alcohols, and the like. The aqueous dispersion is 
undesirable because of its great instability resulting from sudden changes 
in temperature. It is desirable that it be maintained as a homogeneous 
solution for use. 
SUMMARY OF THE INVENTION 
We have discovered a method for the one-step preparation of Compound III 
which facilitates the handling of the by-product metal halide and provides 
the product in an immediately usable form without further formulation or 
treatment. More particularly, we have discovered that by reacting a halide 
of formula I and a metal compound of formula II in N-methylpyrrolidone, 
the reaction proceeds relatively rapidly to completion and the by-product 
metal halide precipitates from the solution. The product, Compound III, 
remains dissolved in the reaction solution. Because of the compatibility 
of N-methylpyrrolidone with environmental systems, the Compound III in 
solution may be used directly without further treatment. Moreover, the 
metal halide by-product is easily separated by precipitation and 
filtration and can be re-used. 
DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention is carried out by mixing 
N-methylpyrrolidone with Compounds I and II at a temperature and for a 
period of time sufficient to complete the reaction. The completion of the 
reaction is evidenced by the disappearance of one of the reactants. 
Thereafter, the reaction mixture is cooled and filtered to remove 
precipitated metal halide. The filtrate may be used as is and typically, 
would contain concentrations of Compound III in the range from about 5 to 
25% by weight. Conversions are in the range from about 70 to 90%, based on 
the weight of starting halide (Compound I). The recovery of the metal 
halide is generally in the range from about 80 to 90%. Of course, 
additional conventional surface active agents or other adjuvants can be 
added to the reaction solution, 
The present process is advantageous inasmuch as a separate formulation step 
is not required and the expensive metal halide is recovered. Also, no 
water is required for the reaction and there is no need to displace any 
aqueous halide salt. This results in improved economics for the process. 
In addition, we have found that the reaction can be carried out at 
relatively low temperatures in the range from about 40.degree. to 
60.degree. C. Preferably, the reaction is carried out at about 50.degree. 
C. The time period for the reaction to go to completion can be from about 
20 minutes to 24 hours depending on the temperature. The higher the 
temperature, the more rapid the reaction. The preferred time period is 
from about 20 minutes to 6 hours. 
The reactants are normally added in essentially a stoichiometric ratio of 
about 1 mole of Compound I to 1 to 3 moles of Compound II. A ten to twenty 
percent excess of the materials may be used. 
A catalyst is not needed since the solvent appears to have a catalytic 
effect. Normally, the amount of the N-methylpyrrolidone used is from about 
1 to 5 times the weight of the reactants. Preferably, the amount of 
solvent used is equivalent to the combined weight of the alkyl dihalide 
and thiocyanate salt. 
The following example illustrates the invention:

EXAMPLE 1 
A four-necked 500 ml round-bottom flask was fitted with a magnetic stirrer, 
thermometer, two water condensers, and a nitrogen gas inlet and outlet. It 
was charged with 50.63 grams of NaSCN (0.63 moles) and 100 grams of 
N-methyl-2-pyrrolidone (1 mole). The mixture formed a pasty slurry and its 
temperature increased to about 50.degree. C. 45.15 grams (0.26 moles) of 
methylene dibromide was admixed to the slurry over a period of twenty 
minutes while the reaction mixture was maintained under nitrogen gas at 
about 53.degree. C. The reaction mixture maintained at this temperature 
for an additional 24 hours. After this time, practically all of the 
methylene dibromide had reacted as determined by gas chromatography. 
A white precipitate settled to the bottom of the flask and this was 
separated by suction filtration. The precipitate was sodium bromide. The 
amount of sodium bromide produced and gas chromatography analysis of the 
filtrate confirmed that the yield of methylene dithiocyanate was 83%. 
A portion of the filtrate (28 grams) was used to isolate the product. This 
was achieved by adding water slowly to the filtrate. When six grams of 
water had been added, the methylene thiocyanate began to precipitate. 
After 35 grams of water had been added, the product was completely 
precipitated from solution. This product was separated and dried. It 
weighed 5.0 grams and melted at 102.degree.-104.degree. C. Gas 
chromatography of the purified product in N-methylpyrrolidone showed 1 
peak other than the solvent peak. .sup.1 H.sub.nmr, and .sup.13 C.sub.nmr 
and infrared spectra were identical with that of a known pure sample of 
methylene bisthiocyanate. The product yield based on the total recovered 
methylene bisthiocyanate was 73%. The estimated purity of the product was 
99+%. This cyanate was determined spectrophotometrically. See "Standard 
Methods" for the Examination of Water and Waste Water, 16th Ed. (1985); 
American Assoc. of Public Health, American Water Works Assoc.; Water 
Pollution Control Federation; Editors; Greenberg, A.E., et al - pages 
348-350. 
EXAMPLE 2 
The same procedure of Example 1 was used. A reaction flask was charged with 
16.40 grams of NaSCN (0.203 mole), 18.82 grams of CH.sub.2 Br.sub.2 (0.108 
mole) and 100 grams N-methyl-2-pyrrolidone. The temperature rose to 
39.degree. C. from an initial 25.degree. C. upon addition of the reagents. 
It took one hour for all the solids to dissolve while stirring with a 
mechanical stirrer. After a period of 72 hours standing at room 
temperature under N.sub.2 with mild stirring, analysis of the reaction 
mixture showed 38% reaction completion of the reaction via .sup.- SCN 
consumption as well as isolation of methylene bisthiocyanate from an 
aliquot of the reaction mixture. 
EXAMPLE 3 
Example 2 was repeated using 16.17 grams (0.1996 mole) of NaSCN, 17.50 
grams of CH.sub.2 Br.sub.2 (0.1006 mole) and 99.6 grams of 
N-methylpyrrolidone. The temperature was maintained at 54.degree. to 
62.degree. C. for a period of 5 hours. Analysis of the reaction mixture 
via GC analysis showed 8% of the total CH.sub.2 Br.sub.2 remained and a 
yield of 61% of methylene bisthiocyanate. The .sup.- SCN consumption was 
monitored by determination of .sup.- SCN spectrophotometrically as 
described in "Standard Methods" for the Examination of Water and Waste 
Water, 16th Edition (1985), American Public Health Assoc., American Water 
Works Assoc., Water Pollution Control Federation, Editors: Greenberg, A. 
E., et al pages 348-350.