Process for preparing tetrahydrocarbylphosphonium bicarbonate salts

Certain tetrahydrocarbylphosphonium bicarbonate salts are produced by reacting a trihydrocarbyl(hydrocarbylcarboxymethyl)phosphonium hydroxide inner salt with water. For example, methyl tri-n-butylphosphonium bicarbonate salt was prepared in quantitative yields by heating tri-n-butylcarboxymethylphosphonium hydroxide inner salt in an aqueous methanol solution at 100.degree. C. for 3 hours.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the preparation of a tetrahydrocarbylphosphonium 
bicarbonate salt from a 
trihydrocarbyl(hydrocarbylcarboxymethyl)phosphonium hydroxide inner salt. 
2. Description of the Prior Art 
The preparation and reactions of certain phosphobetaines were described by 
Denney et al., J. Org. Chem., Vol. 27, pp. 3404-3409 (1962). This 
reference discloses that triphenyl(carboxyethyl)phosphonium hydroxide 
inner salt, a so-called phosphobetaine, is soluble in water, but does not 
disclose the occurrence of any reaction between these components 
elucidated in the determination of the chemical properties of these 
compounds. 
SUMMARY OF THE INVENTION 
It has now been discovered that certain tetrahydrocarbylphosphonium 
bicarbonate salts are prepared in a process comprising reacting (a) a 
trihydrocarbyl(hydrocarbylcarboxymethyl)phosphonium hydroxide inner salt 
represented by the formula 
##STR1## 
in which R.sub.1 -R.sub.3 are each independently hydrocarbyl or 
inertly-substituted hydrocarbyl radicals having from 1 to about 20 carbon 
atoms, and R.sub.4 is phenoxy, phenyl, hydrogen or an alkyl having from 1 
to about 20 carbon atoms, with (b) water. The tetrahydrocarbylphosphonium 
bicarbonate salts are extremely useful catalysts for promoting the 
reaction between (1) vicinal epoxides and (2) phenols or carboxylic acids 
or anhydrides. These novel salts can be represented by the formula 
##STR2## 
DETAILED DESCRIPTION OF THE INVENTION 
The reactants in the instant process are known classes of compounds. 
Trihydrocarbyl(hydrocarbylcarboxymethyl)phosphonium hydroxide inner salts 
and methods for their preparation are described in U.S. Pat. No. 
4,048,141, the relevant portions of which are incorporated herein by 
reference. The compound of formula I can be conveniently prepared by 
reacting a trihydrocarbyl phosphine with a substituted 
.alpha.-chloroacetic acid represented by the formula 
##STR3## 
wherein R.sub.4 is as previously mentioned, followed by treatment with a 
base. This method of preparation is particularly advantageous where 
R.sub.4 is H. A salt of a substituted or unsubstituted 
.alpha.-chloroacetic acid can be employed in the aforementioned method in 
place of the .alpha.-chloroacetic acid, in which case no base treatment is 
necessary. Preferably, this salt is a sodium salt. 
It is essential in this preparation that the phosphobetaine reactant 
(depicted in formula I) contain as little residual halogen ion from the 
starting materials as possible (preferably less than 1 percent by weight), 
as halogen ions can produce undesirable by-products during the reaction of 
the phosphobetaine. The use of a commercial ion-exchange resin in the 
tertiary amine or hydroxide forms as the base in the preparation of the 
compound of formula I minimizes the presence of halogen ions in the 
product. Alternatively, the phosphobetaine solution can be subjected to 
electrodialysis to reduce the presence of these halide ions to acceptable 
levels. 
When R.sub.4 is an alkyl, phenyl or phenoxy group, the above-described 
method of preparation of compounds represented by formula I is frequently 
of low yield. A potentially more efficient synthetic route in these 
instances is to react a C.sub.1 -C.sub.4 alkyl ester of a substituted 
.alpha.-haloacetic acid with a trihydrocarbyl phosphine in an inert liquid 
reaction medium such as diethyl ether. The resulting 
tetrahydrocarbylphosphonium halide (wherein one of the hydrocarbyl groups 
is a methylenecarboxylate ester) is reacted with dilute hydrochloric acid 
to hydrolyze the ester in the following manner (wherein R.sub.1 -R.sub.3 
are as aforementioned; R.sub.4 is alkyl, phenyl or phenoxy, R.sub.5 is 
C.sub.1 -C.sub.4 alkyl and X is a halide ion): 
##STR4## 
The reaction is conducted at elevated temperatures to distill off the 
alkanol by-product and drive the reaction to substantial completion. The 
compound represented by formula III is then contacted with a commercial 
ion-exchange resin (in the hydroxide or tertiary amine form) to produce a 
compound corresponding to formula I. 
The hydrocarbyl moieties, R.sub.1 -R.sub.3, borne by the compound of 
formula I, are univalent hydrocarbon radicals which may be the same or 
different and which may bear substituents inert in the instant reaction. 
For example, R.sub.1 -R.sub.3 can be alkyl (such as methyl, ethyl, propyl, 
dodecyl), aryl (such as phenyl), alkaryl (such as a dodecylbenzene 
radical), aralkyl (such as benzyl, phenylethyl), hydroxyalkyl or 
cyanoalkyl. Preferably, R.sub.1 -R.sub.3 are each independently phenyl or 
a C.sub.1 to C.sub.12 alkyl group and more preferably are each 
independently phenyl or a C.sub.1 to C.sub.4 alkyl group. Most preferably 
R.sub.1 -R.sub.3 are each phenyl or n-butyl. R.sub.4 is preferably methyl 
or hydrogen, most preferably hydrogen. 
The stoichiometry of the subject reaction requires at least one mole of 
water per mole of the compound of formula I. An excess of water is 
preferred to insure complete reaction of the phosphobetaine reactant. 
The reaction can be conducted either neat or in a liquid inert organic 
diluent. By the term "inert" is meant, once again, inert in the instant 
process. Suitable diluents include water, water-miscible lower alkanols 
(C.sub.1 -C.sub.4) and mixtures of such lower alkanols with aromatic 
hydrocarbon solvents, such as benzene or toluene. Preferably, the instant 
process is conducted with no diluent other than the reactants themselves 
(i.e., neat) or methanol is employed as a diluent. The instant reaction 
can also be conducted with the reactant of formula I in the solid phase 
and the water reactant present in the vapor phase or adsorbed on the solid 
phosphobetaine reactant. The phosphobetaine reactant is hygroscopic. 
However, reaction in the liquid phase is preferred. 
The order of addition or method of contacting the reactants is not critical 
and may be varied to convenience. Substantially any reaction temperature 
from about 20.degree. to about 125.degree. C. can be used to advantage, 
preferably about 50.degree. to about 100.degree. C. Typically, the 
reaction rate will be more rapid at higher temperatures within the 
aforementioned ranges. Lower reaction temperatures than the foregoing are 
operable, but require uneconomically long reaction times. 
The reaction time for the rearrangement to the phosphonium bicarbonate salt 
is dependent upon the identity of R.sub.1 -R.sub.3 borne by the reactant 
represented by formula I. For example, at 25.degree. C. a methanol 
solution containing an equivalent quantity of the 
triphenylcarboxymethylphosphonium hydroxide inner salt and water is 
quantitatively converted to the corresponding bicarbonate salt after 240 
hours. In contrast, the analogous tri-n-butyl derivative is stable in an 
aqueous methanol solution at 25.degree. C. for more than 6 months. 
The atmosphere above the reactants is desirably inert in the reaction. 
Where the water reactant is adsorbed on the solid compound of formula I, 
the reaction should be conducted at a pressure of less than 20 millimeters 
of mercury. The pressure above the reactants in the liquid phase is not 
critical, so long as the reactants are maintained in intimate contact. 
In the liquid phase reaction, the pH of the reaction medium should be at 
least about 7, preferably 8 or greater.

Experimental: 
The following examples are illustrative of the present invention. All parts 
and percentages are by weight, unless otherwise specified. 
EXAMPLE 1 
A solution of 647.25 grams (6.85 moles) of monochloroacetic acid in 161.84 
grams of water was added dropwise over a period of 1.5 hours to a stirred 
solution of 1400.0 grams (6.776 moles) of tri-n-butyl phosphine in 74.7 
grams of water under a nitrogen atmosphere. The temperature of the 
reaction mixture was controlled so as not to exceed 35.degree. C. The 
reaction mixture was stirred for an additional 30 minutes at 
25.degree.-35.degree. C. and then was heated to 85.degree. C. for 2 hours 
in the presence of air. The reaction yielded 2242.0 grams of a clear, 
colorless solution, which was found by infrared spectroscopy and proton, 
phosphorus-31 and carbon-13 nuclear magnetic resonance spectroscopy to 
contain 88.8 percent tri-n-butyl(carboxymethyl)phosphonium chloride. 
A portion of the above-described aqueous product solution containing 610.0 
grams (1.825 moles) of tri-n-butyl(carboxymethyl)phosphonium chloride was 
added with stirring to 164.0 grams (5.12 moles) of methanol. This methanol 
solution was then contacted immediately with an excess of a commercial 
ion-exchange resin either as the hydroxide or the tertiary amine form at 
20.degree. C. to produce a solution pH greater than 7. The solution was 
filtered to remove the ion-exchange resin. A proton magnetic resonance 
analysis of the filtrate confirmed that virtually quantitative conversion 
to the tri-n-butyl(carboxymethyl)phosphonium hydroxide inner salt had 
occurred. The methanol solution of this phosphobetaine was distilled at 
50.degree. C. at reduced pressure (0.1 millimeter mercury). The resulting 
viscous, hygroscopic liquid was heated at 25.degree. C. under vacuum for 2 
weeks to produce a colorless crystalline solid, which was identified as 
substantially pure tri-n-butylmethylphosphonium bicarbonate salt by 
nuclear magnetic resonance spectroscopy, infrared spectroscopy and 
elemental analysis. 
EXAMPLE 2 
Solid monochloroacetic acid (76.0 grams, 0.80 mole) was added rapidly at 
25.degree. C. to a stirred solution of triphenylphosphine (104.0 grams, 
0.40 mole) in 120 milliliters of toluene under a nitrogen atmosphere. 
After 30 minutes, the reaction mixture was slowly heated to 42.degree. C. 
to dissolve the monochloroacetic acid and was stirred vigorously at this 
temperature for about 2 hours. The stirring was stopped and the mixture 
separated into two phases. After 12 hours at 25.degree. C. the bottom 
phase crystallized to a white solid, which was collected, washed with 
diethyl ether and air dried to yield 125.0 grams of a white solid product. 
The infrared and phosphorus-31 and proton nuclear magnetic spectrums and 
the elemental analysis of this product determined its identity to be 
triphenylcarboxymethyl phosphonium chloride chloroacetic acid complex. 
The white solid product described immediately above was dissolved in an 
81.0 gram solvent mixture of 95 percent methanol and 5 percent water. This 
aqueous methanol solution was then percolated slowly through a column 
containing an excess of a commercial ion-exchange resin in the tertiary 
amine form to produce a solution having a pH greater than 7.0. The 
methanol solvent was distilled at 0.degree. C. at reduced pressure to 
yield a white solid product, which was then washed with diethyl ether and 
air dried. This white solid was identified by conventional methods of 
analysis as the triphenyl(carboxymethyl)phosphonium hydroxide inner salt. 
The triphenyl(carboxymethyl)phosphonium hydroxide inner salt (75 grams) in 
a 366 gram solution of 95 percent methanol and 5 percent water was heated 
at 100.degree. C. for 30 minutes. The methanol solvent is distilled at 
25.degree. C. under reduced pressure to yield 79 grams of a white solid. 
The product is identified by proton, carbon-13 and phosphorus-31 nuclear 
magnetic resonance and infrared spectroscopy as methyltriphenylphosphonium 
bicarbonate salt. 
Utility: 
To a reaction vessel equipped with stirring means and temperature 
indication and recording means was charged 6.6 grams of the diglycidyl 
ether of bisphenol A (DGEBA) having an epoxy equivalent weight of 187, 
3.40 grams of bisphenol A and 0.0066 gram (0.1 part per hundred of resin) 
of triphenylmethylphosphonium bicarbonate salt at room temperature. The 
stirred mixture was heated to 150.degree. C. and thereafter allowed to 
freely exotherm with no external heat applied. After the temperature of 
the mixture had peaked, heating was resumed for 2 additional hours to 
maintain a temperature of 180.degree. C. 
The observed epoxy content of the resin product determined by conventional 
wet analysis technique was 2.20 percent. The observed epoxy content was 
slightly greater than the theoretical epoxy content of 2.15 percent. A 
substantially linear epoxy resin of excellent color was provided. 
This reaction demonstrates the utility of tetrahydrocarbylphosphonium 
bicarbonate salts as catalysts in the preparation of epoxy resins.