Tertiary butyl hydroperoxide, a well-known commercial chemical produced by the liquid phase oxidation of isobutane, is useful for various purposes, for example, as a chemical intermediate and as a free radical polymerization initiator for vinyl monomers. A typical process for the liquid phase oxidation of isobutane employing a molecular oxygen-containing gas is described in Winkler et al U.S. Pat. No. 2,845,461. Tertiary butyl hydroperoxide resulting from this process is produced in admixture with tertiary butyl alcohol, a by-product of the oxidation reaction, together with minor amounts of other oxidation products such as acetone, formic acid, other alcohols and esters of formic acid and the like, as well as primary and secondary alkyl hydroperoxide contaminants. The tertiary butyl hydroperoxide product can be separated from a majority of these by-products by fractional distillation as described in U.K. Pat. No. 1,232,709, wherein the distillation is effected in the presence of a diluent vapor, or is recovered as a bottom stream in a distillation process utilizing a reflux agent, as described in Herzog U.S. Pat. No. 3,427,229. A disadvantage encountered in distillations of isobutane oxidation mixtures is that there tends to occur significant decomposition of the tertiary butyl hydroperoxide, thereby contaminating the desired tertiary butyl hydroperoxide product with additional quantities of oxygen-containing decomposition products; hence, in an effort to avoid hydroperoxide decomposition, processes have been suggested whereby the distillation is carried out in the presence of a material which is capable of maintaining the effective pH of the liquid fraction during the distillation below about 9, and preferably below about 8, as disclosed in Harvey U.S. Pat. No.3,449,217.
It has been proposed in Farkas et al U.S. Pat. No. 2,430,864 to effect oxidation of certain cyclic hydrocarbons to produce saturated cyclic hydrocarbon hydroperoxides in the presence of a basic compound, thereby forming salts with acids which are produced during the oxidation, thus effectively removing acids which appear to be catalysts for the decomposition of peroxides. It has also been suggested by D. E. Winkler et al, Industrial Engineering Chemistry, 53, 655-658 (1961) to rinse the oxidation reactor employed in the oxidation of isobutane for the production of tertiary butyl hydroperoxide with a dilute solution of sodium pyrophosphate which serves as a neutralizer and metal ion scavenger.
In U.K. Pat. No. 1,232,710, dated Sept. 15, 1971, treatment of tertiary butyl hydroperoxide, obtained by the molecular oxygen-containing gas oxidation of isobutane, with from about 0.05 to about 1 milliequivalents of an inorganic base, organic amine, or basic ion exchange resin, per gram of hydroperoxide; i.e. an amount sufficient to avoid a highly alkaline pH which would cause the hydroperoxide to react; according to this patent, the product hydroperoxide preferably has a pH in water close to 7 for final storage, the function of the base being stated to be for removal of metal formate, t-butyl formate and formic acid. U.K. Pat. No. 957,952 discloses the hydrolysis of neutral impurities admixed with specified organic peroxides by contacting the peroxide with ammonia.
Rosenthal et al U.S. Pat. No. 3,445,523 discloses that organic hydroperoxide, illustratively tertiary butyl hydroperoxide, may be stabilized with an aqueous mixture of (1) sodium or potassium hydroxide and (2) sodium or potassium dihydrogen phosphate, the pH of the hydroxide and the aqueous mixture being in the range of between 7 and 8.
Still other methods of purification of organic peroxides described in the literature include precipitation from concentrated alkali, as described by A. G. Davies et al, J. Chem. Soc. page 2204-2209 (1954) or by derivatization with an appropriate reagent, as described by A. Rieche et al, Chem. Berichte, 92 beginning at page 2239 (1959). However, separation of tertiary butyl hydroperoxide from isomeric hydroperoxide contaminants is not specifically disclosed in either of these disclosures and both methods require extensive work up, namely, isolation and subsequent regeneration of tertiary butyl hydroperoxide from the formed derivatives.
In an effort to satisfy the demand for aqueous solutions of tertiary butyl hydroperoxide exhibiting performance characteristics suitable for use as an intermediate for the production of t-butyl peresters, employable as initiators in polymerization reactions, Borchert et al U.S. Pat. No. 3,773,687 suggests the stabilization of aqueous solutions containing about 60 to 75 weight percent of tertiary butyl hydroperoxide by maintaining the aqueous solution at a temperature of from about 45.degree. C. to about 80.degree. C. for from 0.5 to 10 days. A more recent method for purification of tertiary butyl hydroperoxide described in Worrell et al U.S. Pat. No. 3,864,216 involves azeotropic distillation of diluted isobutane oxidation products from water, which method also employs small quantities of caustic to neutralize carboxylic acids incidental to the oxidation process.
However, all of the aforementioned methods are deficient in providing a tertiary butyl hydroperoxide product having acceptable performance characteristics, as an intermediate for the production of t-butyl peresters, due to the presence of primary and secondary alkyl hydroperoxide contaminants which, in the Worrell et al process, for exampIe, co-distill with the desired tertiary butyl hydroperoxide. Oxygenated derivatives produced from such contaminated t-butyl hydroperoxide product suffer loss in assay and produce deleterious decomposition products which compromise their usage as intermediates in the production of t-butyl peresters, for example, which are useful as polymerization initiators.
Thus, it is a principle object of the present invention to provide an improved process for the purification of tertiary butyl hydroperoxide obtained from isobutane oxidation reaction mixtures.
It is another object of this invention to provide a process for the purification of tertiary butyl hydroperoxide obtained from isobutane oxidation without introduction of additional acidic components.
It is a further object of the present invention to provide a process for the purification of tertiary butyl hydroperoxide obtained from the liquid phase molecular oxygen-containing gas oxidation of isobutane, contaminated with primary and secondary alkyl hydroperoxides.
A still further object of the present invention is to provide a method for preparing tertiary butyl hydroperoxide having improved stability and uniformity, particularly in connection with its use as an intermediate in the production of tertiary butyl perester polymerization initiators.
Further objects will become apparent from the following detailed description and claims.