Phosphonium Catalysts for Hydroxyalkylation of Phenols or Thiophenols

The present invention relates to a process for the preparation of hydroxyalkylphenyl ether or thioether compounds. More particularly, the present invention is concerned with improved catalysts for use in the preparation of such compounds by the reaction of cyclic organic carbonate compounds with phenols and thiophenols.

Carlson disclosed in U.S. Pat. No. 2,448,767 a method of hydroxyethylation wherein ethylene carbonate or ethylene sulfite was reacted with certain organic compounds including phenols and alcohols. The reaction could be carried out in the presence or in the absence of a suitable solvent, and in the presence or in the absence of a suitable catalyst. Catalysts that were disclosed included an acid (concentrated sulfuric acid or an alkyl ester of sulfuric acid), a base (alkali carbonates), or the alkali salt of a phenol. The preferred catalyst was an alkali carbonate or alkali salt of a phenol. U.S. Pat. No. 3,283,030 disclosed use of potassium carbonate as a basic catalyst in the reaction of ethylene carbonate with certain substituted phenols.

Alkali metal hydrides disclosed by U.S. Pat. No. 2,987,555 and alkali metal hydroxides disclosed by U.S. Pat. No. 2,967,892 have also been found to be effective catalysts for hydroxyalkylation reactions of ethylene carbonate with phenols and chloromethylethylene carbonate with phenols respectively.

One disadvantage associated with prior art processes using acidic or basic catalysts is the inability to use certain modified phenolic or thiophenolic compounds that are unstable under acidic or basic reaction conditions. A further disadvantage of known prior art processes is that for many purposes the catalyst must be removed from the reaction products, necessitating a subsequent purification process with its attendant expense. It would be advantageous to provide a catalyst that effectively promotes the reaction under essentially neutral conditions and which is otherwise substantially unreactive so that its presence in the final product is not disadvantageous.

This invention comprises an improved process for the hydroxyalkylation of phenols or thiophenols providing high yields with good selectivity. In particular the invention comprises the use of phosphonium salts as reaction catalysts for the reaction of phenols or thiophenols and cyclic organic carbonate compounds. The phosphonium salts of the instant invention are considered to be less acidic or basic than the previously known and employed catalysts thereby allowing utilization of reactants having a greater variety of functionality than has been possible under prior known methods. The hydroxyalkylphenyl ether or thioether products formed according to this invention are used as solvents and in certain coatings as well as in additional industrial applications.

This invention lies in the discovery that phosphonium salts act as effective catalysts in the reaction of cyclic organic carbonate compounds with phenols or thiophenols.

The phosphonium salts for use according to the instant invention are of the formula R.sub.4 P.sup.+ X.sup.- wherein R is selected from phenyl and C.sub.1-4 alkyl; and X.sup.- is a negative counterion or one equivalent portion of a polybasic anion. Preferably X.sup.- is bicarbonate, acetate, halide or R'O.sup.- wherein R' is hydrogen, C.sub.1-4 alkyl or a C.sub.6-20 radical selected from aryl and alkyl, aralkyl, hydroxy, alkoxy, hydroxyaralkyl and alkoxyaralkyl-substituted derivatives thereof.

The amount of catalyst required to effectively catalyze the hydroxyalkylation reaction according to the present invention may vary compared to total reactant weight from about 0.1 percent to about 10.0 percent depending on the particular catalyst. It is preferred to employ the catalyst in amounts from about 0.5 percent to about 2.0 percent by weight.

The catalyst of this invention may be used by itself or in combination with other known hydroxyalkylation catalysts.

The phenol- or thiophenol-containing compounds that may be hydroxyalkylated by organic carbonate compounds according to this invention are extremely varied. Carlson in U.S. Pat. No. 2,448,767 discloses a wide variety of reactive hydrogen-containing aromatic compounds including phenol, thiophenol, alkaline salts of phenol, .beta.-naphthol, and 8-hydroxyquinoline that are capable of undergoing hydroxyalkylation with alkyl carbonate compounds. Additionally Carlson taught that all such compounds tested responded to the hydroxyalkylation reaction and it was believed all such compounds would be responsive.

Davis in U.S. Pat. No. 2,987,555 discloses an additional number of phenols that may be hydroxyalkylated by reaction with alkylene carbonates including: p,p'-biphenol, p,p'-sec-butylidene diphenol, 4,4'-isopropylidenebis(o-cresol), 4,4'-isopropylidenebis(2-phenylphenol), o-chlorophenol, o-cresol, p-propylphenol, p-bis(o-cresol) and the like.

We have found that nearly any phenol- or thiophenol-containing reactant is suitable for use according to this invention. Included are: phenol, thiophenol, and phenol or thiophenol compounds substituted with one or more hydroxy, mercapto, alkyl, aryl, alkaryl, aralkyl, halo or sulfonyl substituents or mixtures thereof.

However, Tsuruya disclosed in J. Polymer Sci., Part B, 7, 709 (1969) that 2,4,6-tribromophenol, preferably forms polymers through debromination when reacted with organic carbonate compounds. This compound therefore is not considered to be suitable for use according to the present invention.

The cyclic organic carbonates used in the hydroxyalkylation reactions according to this invention may likewise be varied. In addition to ethylene carbonate, Davis in U.S. Pat. No. 2,987,555 disclosed that any cyclic alkylene carbonate having the appropriate carbonate moiety attached at adjacent positions was capable of undergoing hydroxyalkylation with phenolic compounds. Specifically mentioned carbonate compounds were propylene carbonate, 1,2- or 2,3-butylene carbonate and phenylethylene carbonate. For said disclosure this teaching is herein incorporated by reference.

In addition, ethers of alkylene carbonates of the formula ##STR1## wherein R is C.sub.1-20 alkoxy, alkoxyalkylene or (poly)alkoxyalkylene may also be used.

As previously mentioned, use of the instant catalyst at a substantially neutral pH in the practice of this invention instead of acidic or basic catalysts advantageously permits the use of reactants containing greater functionality. The catalyst and milder reaction conditions additionally allow greater selectivity in product formation including the exclusive formation of the monohydroxyalkylated product without concomitant formation of secondary reaction products.

The reaction may take place in the presence or absence of an inert solvent. In the preferred embodiment the cyclic carbonate reactant is a suitable solvent.

The reactants may be combined in nearly any molar ratio since some product is produced under nearly all conditions. It is preferred however, to combine the reactants in a stoichiometric ratio thereby eliminating the need to remove excess reactants from the finished product in a subsequent purification step.

The reaction may be carried out in any vessel suitably designed to contain the reactants and products and be unreactive under the conditions of the invention. Representative of suitable reaction vessels are those made of glass, stainless steel or other unreactive material.

The reaction may be run in the practice of this invention at any suitable temperature from about 100.degree. C. to about 210.degree. C. Faster reaction rates are observed at higher temperatures but decomposition of reactants and products is likely to occur at the higher temperatures. The optimum temperature for particular reactants allowing fast reaction rates, but minimizing decomposition side-products may be easily determined according to ordinary techniques of experimentation. The preferred operating temperature for most phenolic and carbonate reactants is from about 150.degree. C. to about 170.degree. C. Heating the reaction vessel to the operating temperature may conveniently be occasioned by any usual means such as a heat lamp, heating mantle, oil bath, etc.

The time for the reaction to proceed to substantial completion will vary depending on various factors such as the particular phenol- or thiophenol-containing reactant, cyclic organic carbonate reactant, and temperature selected. Generally about two hours to about five hours is sufficient. The evolution of carbon dioxide is a convenient indicator of the progress of the reaction.

The reaction may be run either accompanied by mechanical or magnetic stirring or without stirring. To avoid liquid entrapment during the evolution of carbon dioxide it is also advantageous to employ a condenser according to well-known techniques in the art.

The product, a corresponding hydroxyalkyl ether or thioether derivative may be easily recovered from the reaction mixture, for example, by distillation if a liquid, or by recrystallization if a solid.

While the invention has been described as useful in a batch process reaction, it may be utilized equally advantageously in a continuous reaction process.

Having described the invention the following examples are given merely as illustrative of the present invention and are not to be considered as limiting.

Ethylene carbonate (45 g, 0.51 mole), phenol (47.1 g, 0.5 mole) and 5 g of the phosphonium catalysts identified in Table I were placed in a 250 ml glass round-bottomed flask equipped with a condenser and gas bubbler. Agitation was provided with a magnetic stirrer. The mixture was heated to 160.degree. C..+-.2.degree. C. in an oil bath. After the time indicated in Table I, the reaction vessel was removed from the oil bath and purified by distillation. The major product was identified as 2-phenoxyethanol. In all cases small amounts less than 10 percent of higher oligomeric reaction products were also identified. Results are provided in Table I.