PREPARATION OF 2,6-DIALKYL PHENOXYDIHALOPHOSPHITES

Abstract: A process involving the reaction of a 2,6- dialkylphenol with a phosphorus trihalide, preferably phosphorus trichlor­ ide. The reaction is catalyzed by a tertiary amine, a quaternary ammonium halide, a tertiary phosphine or a quaternary phos­ phonium halide.

Description: PREPARATION OF HINDERED PHENOXY DICHLOROPHOSPHITES DESCRIPTION This invention relates to a process for preparing hindered phenolic phosphites. More particularly it relates to such a process which is characterized by its use in catalytic quantities of a compound previously used as a reactant in this type of process. Hindered phenoxy dichlorophosphites are useful as intermediates in the preparation of polymer stabilizers, lubricating oil additives, flame-retarding agents and the like. The chlorine atoms are reactive with compounds containing an active hydrogen atom, or the salts thereof, for example, to form products which act to supress the formation of corrosion products in polymer compositions. These hindered phenoxy dichlorophosphites have in the past been prepared by the reaction of phosphorus trichloride with the appropriate alkylphenol, in the presence of molar amounts of a tertiary amine. The tertiary amine acts as a halogen acid acceptor. Thus, U.S. 3,271,481 (Kujawa et al) shows the reaction of phenols, substituted in at least two of their positions with organic radicals containing at least four carbon atoms, with a phorphorus trihalide in the presence of a sufficient quantity of tertiary amine to react with all of the hydrogen halide liberated in the reaction. Phenols disclosed include 2,6-ditertiarybutyl phenol; phosphorus trichloride is the preferred phosphorus trihalide. U.S. 3,412,118 {Kujawa et al) shows much the same differing principally in that it claims salts of phosphites derived from the dichlorophosphites prepared as above. U.S. 3,402,196 (Dannels et al) shows the reaction of a substituted phenol such as 2,6-ditertiarybutylphenol with phosphorus trichloride to for the expected dichlorophosphite. An amine, preferably a tertiary amine such as triethylamine, is used as a halogen acid acceptor. The resulting dichlorophosphite then is converted either to the corresponding 4-hydroxyphenyl phosphonous acid or bis (4-hydroxyphenyl) phosphonous acid. U.S. 2,843,616 (Hordy et al) shows a method for preparing trialkyl phosphites involving the catalyzed reaction of phosphorus trichloride or phosphorus tribromide with an alcoholate. The catalyst is a tertiary amine such as tributylamine. The alcoholates are those having 1-4 carbon atoms. Comparative experiments show that the catalyst improved the yield of trimethyl phosphite from 17% to 52% of the theory. None of the above patents, however, show the catalyzed reaction of a phosphorus trihalide with a hindered phenol to give good yields of a dichlorophosphite product. Heretofore it apparently has been believed necessary that the hydrogen halide formed in such a process had to be converted to an amine salt as it was formed According to the present invention there is provided a process for the preparation of a dichlorophosphite comprising reacting equal molar quantities of a 2,6-dialkylphenol having the structure: EMI3.1 wherein R is hydrogen or methyl, R1 is a tertiary alkyl group of 4-8 carbon atoms, and R2 is an alkyl group of 1-8 carbon atoms, and a phosphorus trihalide in the presence of a catalytic amount of a tertiary amine, a quaternary ammonium halide, a tertiary phosphine or a quaternary phosphonium halide. The reaction may be carried out simply by mixing the 2-6-dialkylphenol, phosphorus trihalide and catalyst and heating the mixture until the reaction is completed. Generally, under such conditions the reaction ceases after about 10-20 hours. An alternative method involves sparging the phosphorus trihalide into the heated mixture of 2,6-dialkylphenol and catalyst. This allows the reaction to be carried out at a higher temperature when, as is the usual and preferred case, the phosphorus trihalide is phosphorus trichloride. A higher temperature in turn results in a faster reaction and a shorter reaction time. The same result, i.e., a shorter reaction time, can be achieved by carrying out the reaction under pressure. The higher pressure permits a higher reaction temperature which increases the reaction rate. G pressure of 0-150 psig (-11,5 kg/an?) are oantemplRted. When superatmospheric pressure is employed it is advisable to vent the evolved hydrogen chloride from the reaction vessed from time to time. The temperature of the process may range from about 60D to about 1800C. In the usual situation the process temperature will be that of the refluxing reaction mixture, i.e., about 760C when phosphorus trichloride is the phosphorus trihalide, or about 1750C when it is phosphorus tribromide. Phosphorus trichloride, however, is the preferred reactant because of its ready availability and low cost. and the preferred temperature, for a non-pressurized reaction, is within the range of from about 700C to about 85'C. The stoichiometry of the reaction requires one mole of phosphorus trihalide per mol of 2,6-dialkylphenol. Generally, in view of the relative volatility of the phosphorus trihalide reactant, a molar excess of that reactant should be used, e.g., from about 1.05 to about 1.20 molts per mol of 2,6-dialkylphenol. The R1 and R2 groups in the above structural formula of the 2,6-dialkylphenol are as indicated alkyl groups of 1-6 carbon atoms. R1 is a tertiary alkyl group, e.g., tertiarybutyl, 2-methylbutanol-2, 3-methylhexanol-3 and 2-methylhexanol-2. R2, on the other hand, while preferably also a tertiary alkyl group, may be methyl, ethyl, isopropyl, etc. as well. Preferably, though, both R1 and R2 are each tertiary alkyl groups of 4-6 carbon atoms. The reason for this preference is that these more sterically hindered phenols undergo reaction with phosphorus halides only with relative great difficulty and it is thus relatively more important that a catalyst be used. Regardless of the method of carrying out the reaction product may be isolated by evaporating away whatever volatile materials remain, such as unreacted phosphorus halide, then distilling the residue at reduced pressure. The phosphorus trihalide may be either phosphorus trichloride or phosphorus tribromide. The former is preferred because it is much more easily and economically available. The catalyst is an organic nitrogen or phosphorus compound having the structure: R'AX m n p wherein d is a hydrocarbyl group, A is nitrogen or phosphorus, X is chlorine or bromine, m is 3-5, n is 1 or 2, and p is 0 or 1. The catalyst can also be polymeric, e g,. a polymer which contains pendent tertiary amine groups or quaternary ammonium or phosphonium groups. The hydrocarbyl groups represented by R may include aliphatic, aromatic or cycloaliphatic radicals. The hydrocarbyl groups each contain 1-18 carbon atoms. Illustrative examples of suitable hydrocarbyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tertiarybutyl, n-amyl, isoamyl, , n-hexyl, 2-ethylhexyl, n-octyl, n-decyl, n-dodecyl, tridecyl, n-tetradecyl and n-octadecyl; phenyl, alpha-naphthyl, kenyl, p-totyl, 2,4-dimethyiphenyl and n-octylphenyl; benzyl, phenylethyl and 4-phenylbutyl; cyclopentyl, cyclohexyl, 2-methylcyclohexyl and 4-ethyl-cyclohexyl. Hydrocarbyl groups having 1-10 carbon atoms are preferred. The hydrocarbyl group may be divalent, e.g., tetraethylene, pentamethylene, etc.; it may be benzenoid, e.g., as in pyridine or quinoline. As indicated, A is either nitrogen or phosphorus. When A is nitrogen the catalyst is a tertiary amine or a quaternary ammonium halide. When A is phosphorus the catalyst is a tertiary phosphine or a quaternary phosphonium halide. X is a halogen, i.e., either chlorine or bromine. Chlorine is preferred simply because quaternary chlorides are more readily available and less expensive than quaternary bromides. In some instances, i e., where the catalyst is an amine or a phosphine, n is zero -and there is of course no halogen present. Tertiary amines are preferred as catalysts. Illustrative species include pyridine, triethyl amine, tri-n-butyl amine, tri-n-hexyl amine, tris-(2-ethylhexyl) amine, triethylene diamine, diethylene, N,Ndimethyloctadecylamine, quinoline and bis-(1,8-dimethylamino) naphthalene. Other illustrative species include triphenylphosphine, triethylphosphine, tris-(2-ethylhexyl) phosphine, tribenzylmethyl phosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, benzyltriphenylphosphonium chloride, triphenyl -n-propylphosphonium chloride, and tetra-n-hexylphosphonium chloride The catalyst is used in small amounts. From about 0.001 to about 0.10 mol per mol of phosphorus trihalide is suitable. The process of the invention is illustrated by the following examples. EXAMPLE 1 A mixture of 37 g. (0.18 mol) of 2 6-ditertiarybutylphenol, 24.7 g. (0.18 mol) of phosphorus trichloride and five drops of pyridine is heated at reflux temperature (7-5-C) for 5.5 hours, then stripped to a temperature of 150 C. A total of 9 g. of unreacted phosphorus trichloride is recovered. The residue is distilled yielding 16 g. of a fraction which is found, on analysis, to contain 29% of 2,6-ditertiarybutylphenyl dichlorophosphite. Yield: 29% of the theory. EXAMPLE 2 A nixture of 110 g. (0.53 mol) of 2,6-ditertiarybutylphenol, 74.2 g. (0.54 mol) of phosphorus trichloride and 0.3 g. of 1,8-bis(n,µ-divethylasino) naphthalene is heated at reflux temperature for 22 hours, at which point the reflux temperature begins to rise. An additional 39.4 g.(0.29 mol) of phosphorus trichloride is added and heating at reflux temperature resumed for another 15.5 hours. The product mixture is distilled at reduced pressure yielding 67% of the theory of the desired 2,6-ditertiarybutylphenyl dichloro phosphite. EXAMPLE 3 To a mixture of 31 g. (0.15 mol) of 2,6-diter tiarybutylphenol and 0.2 g. of 1,8-bis(N,N-dimethylamino) naphthalene, heated at 150-C, there is sparged, by entrainment with dry nitrogen, 25.4 g. (0..18 mol) of phosphorus trichloride. The phosphorus trichloride is introduced throughout a period of 11.5 hours after which the product mixture is distilled at reduced pressure. Yield: 50% of theory. EXAMPLE 4 A mixture of 36.5 g. (0.22 mol) of 2-methyl- 6- tertiarybutylphenol and 65.5 g. (0.48 mol) of phosphorus trichloride and five drops of pyridine is heated at reflux temperature for 90 minutes whereupon an additional 315 g. (0.23 mol) of phosphorus trichloride and five drops of pyridine are added. Heating at reflux temperature is continued for another two hours. The product mixture is distilled yielding 48 g. of distillate identified as the desired 2-methyl-6-tertiarybutylphenyl dichlorophosphite of 95% purity. EXAMPLE 5 A mixture of 28.5 g. (0.138 mol) of 2,6-ditertiarybutylphenol, 19.0 g. (0.138 mol) of phosphorus trichloride and 0.2 g. of triphenylphosphine are heated at reflux temperature for 26.5 hours. The product mixture is distilled yielding 26.0 g. of distillate. A gas chronomatogram of the distillate shows the presence of 20% of the desired 2,6-ditertiarybutylphenyl dichlorophosphite. EXAMPLE 6 A mixture of 29 g. (0.141 mol) of 2,6-ditertiarybutylphenol, 19.4 g. (0.141 mol) of phosphorus trichloride and 0.2 g. of tributyl allyl phosphonium chloride is heated at reflux temperature for 22 hours. The product mixture is distill-ed yielding 35.5 g. of a distillate which is found upon analysis to contain 80% of the desired 2,6-ditertiarybutylphenyl - dichlorophosphite. Yield: 67% of the theory.

Claims: CLAIMS 1. A process for the preparation of a dichlorophosphite comprising reacting equal molar quantities of a 2,6-dialkylphenol having the structure: EMI10.1 wherein R is hydrogen or methyl, R1 is a tertiary alkyl group of 4-8 carbon atoms, and R2 is an alkyl group of 1-8 carbon atoms, and a phosphorus trihalide, in the presence of catalytic amount of a tertiary amine, a quaternary ammonium halide, a tertiary phosphine or a quaternary phosphonium halide. 2. The process of claim 1 wherein the catalyst is an organic nitrogen or phosphorus compound having the structure: R'A X mnp wherein R' is a hydrocarbyl group, A is nitrogen or phophorus, X is chlorine or bromine, m is 3-5, n is 1 or 2, and p isO O or I. 3. The process of claim 7 wherein the catalyst is a polymer which contains pendent tertiary amine groups or quaternary ammonium or phosphonium groups. 4. The process of claim 1 wherein the catalyst is a tertiary amine. 5. The process of claim 1 wherein the catalyst is a tertiary phosphine. 6. The process of Claim 4 wherein the tertiary amine is an aromatic amine. 7. The process of Claim 1 wherein the catalyst is a quaternary phosphonium halide. 8. The process of Claim 1 wherein the reaction is carried out at a temperature of from about 60-C to about 175it. 9. The process of Claim 1 wherein the phosphorus trichloride is sparged into the mixture of 2,6-dialkylphenol and catalyst. 10. The process of Claim 1 wherein the temperature of the reaction mixture is maintained between about 1250C and about 150*C.

Inventors: ENLOW, WILLIAM PALMER, HECHENBLEIKNER, INGENUIN
Applicants: BORG-WARNER CHEMICALS, INC.
Application year: 1985
Main classification: C07F9
IPC codes: C07F9, C07B61, B01J31