Dimethyl phthalate, hydrolysis

Phthalate esters are widespread contaminants and the dialkyl phthalates are hydrolyzed before degradation of the resulting phthalate (Eaton and Ribbons 1982), which is discussed in Chapter 8, Part 3. For dimethyl phthalate, dimethyl terephthalate, and dimethyl isophthalate only partial hydrolysis may take place (Li et al. 2005). Cocaine is hydrolyzed to benzoate and ecgonine methyl ester by a strain of Pseudomonas maltophilia (Britt et al. 1992). 

Chemical/Physical. Under alkaline conditions, dimethyl phthalate will initially hydrolyze to methyl hydrogen phthalate and methanol. The monoester will undergo hydrolysis forming o-phthalic acid and methanol (Wolfe et al., 1980 Kollig, 1993). A second-order rate constant of 6.9 X 10 /M-sec was reported for the hydrolysis of dimethyl phthalate at 30 °C and pH 8. At 18 °C, the second-order rate constant was 3.1 x lO /M-sec in 1 mM NaOH (Wolfe et al., 1980). Also, hydrolysis half-lives of 3.2 yr was reported at pH 7 and at pH 9 11.6 and 25 d at 30 and 18 °C, respectively (Wolfe et al., 1980). 

The alkaline hydrolysis of phthalate diesters has been fit to the Taft-Pavelich equation (Eq. 9). Dimethyl phthalate (DMP) hydrolyzes to phthalic acid (PA) in two steps DMP + H20->MMP + CH30H and MMP + H20- PA + CH30H. The first step is about 12 times faster than the second, and nearly all the diester is converted to the monoester before product PA is formed. Other diesters are assumed to behave similarly. An LFER was obtained from rate measurements on five phthalate esters (Wolfe et al., 1980b). The reaction constants, p and S, were determined by multiple regression analysis of the measured rate constants and reported values of cr and Es for the alkyl substituents. The fitted intercept compares favorably with the measured rate constant (log kOH = — 1.16 0.02) for the dimethyl ester (for which a and s = 0 by definition). Calculated half-lives under pseudo-first-order conditions (pH 8.0, 30°C) range from about 4 months for DMP to over 100 years for di-2-ethylhexyl phthalate. 

The principal solvolysis reactions for PET are methanolysis with dimethyl terephthalate and ethylene glycol as products, glycolysis with a mixture of polyols and BHET as products, and hydrolysis to form terephthalic acid and ethylene glycol. The preferred route is methanolysis because the DMT is easily purified by distillation for subsequent repolymerization. However, because PET bottles are copolyesters, the products of the methanolysis of postconsumer PET are often a mixture of glycols, alcohols, and phthalate derivatives. The separation and purification of the various products make methanolysis a cosdy process. In addition to the major product DMT, methanol, ethylene glycol, diethylene glycol, and 1,4-cyclohexane dimethanol have to be recovered to make the process economical.1... 

The reagent (1) reacts with dimethyl acetylenedicarboxylate in refluxing benzene with loss of methanol to give an adduct (a) that gives dimethyl 4 -hydroxy-o-phthalate (4) on hydrolysis. Cycloaddition of (1) and p-benzoquinone gives, after acetylation, 1,4,6-triacetoxynaphthalene (5). 

The disappearance of a plasticizer from water can be the result of a number of abiotic and biotic processes that can transform or degrade the compound into daughter compounds that have different physicochemical properties from the parent compound. Hydrolysis is a family of chemical reactions where a plasticizer reacts with water. Phthalate esters may hydrolyze to form monoesters and then dicarboxylic acid. It has been predicted that di-(2-ethylhexyl) sebacate will form 2-ethylhexanol and decanedioic acid. Wolfe et al experimentally measured second-order alkaline hydrolysis rate constants for dimethyl, diethyl, di-n-butyl, and di-(2-ethylhexyl) phthalates, and it appears that hydrolysis may be too slow to have a major impact on the fate of most dissolved plasticizers. The estimated hydrolysis half-lives at pH 7 for 20 plasticizers were longer than 100 days. No information was located for diallyl, ditridecyl and diundecyl phthalates. Under alkaline conditions, hydrolysis may be important for tricresyl phosphate and tri-(2-ethylhexyl) trimellitate at pH 8 their predicted half-lives are 3.2 and 12 days respectively. 

Modifications of the 2-Position. One of the primary objectives of the SAR at the 2-position was to prepare ester, amide, alkyl, aryl and halogen derivatives in place of the cyano functionality. A seemingly obvious route to the carboxylate compounds was tivough the hydrolysis of the 2-cyano of compound 1, but it was found to be umeactive toward hydration, which has been attributed to steric hindrance ( . To synthesize other carboxylate entities at the 2-position, we utilized a reaction analogous to that for the preparation of the carbonitrile, 27a by reacting an alkyl acetate or dimethyl acetamide with molten sodium in diethyl phthalate, to give the sodium salts of... 

Kinetic studies of the alkaline hydrolysis of dimethyl and diethyl phthalate, ethyl benzoate, benzyl cinnamate, and diethyl malonate at 298-313 K in aqueous dioxane were reported. Activation parameters were determined for the alkaline hydrolysis of ethyl octanoate in various mixtures of PrOH-water."... 

Although commercially available, 1-trimethylsilyloxy-1,3-butadiene (1) can be easily prepared by silylation of crotonaldehyde. It has often been used as a reactive diene in Diels-Alder reactions. For example, reaction with dimethyl acetylenedicarboxylate (2) affords the cyclohexadiene diester (3) in 68% yield. This initial Diels-Alder adduct can be converted into two different aromatic products by the proper choice of conditions namely, thermal elimination affords the phthalate (4), while oxidation produces the phenol (5), hoth in good yield (eq 1). Reaction with methyl 3-nitroacrylate (6) followed hy hydrolysis of the initial adduct (7) and elimination of the -nitro group leads to the cyclohexadienol (8) (eq 2). Many other Diels-Alder reactions of this type have been carried out using (1), as shown in Table 1. In general, the endo adduct is favored, especially at lower temperatures. 

Danishefsky s diene with methyl acetylenedicarboxylate gives the phenol, dimethyl 4-hydroxy-<9-phthalate on hydrolysis. 

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