Phthalic acid acidity constants

Physical and Chemical Properties. Tables 5, 6, and 7 bst some of the physical and chemical properties of phthabc acid and its anhydride. Table 5. Physical Constants of Phthalic Acid and Phthalic Anhydride... 

Schwartz et al. [2] investigated the biodegradation of phthalic acid esters adsorbed in river sediments by repeated analysis of the sediment over a two-week period. The di-2-ethylhexyl phthalate content turned out to remain essentially constant (s.d., 5% n=10), irrespective of the absence or presence of a microbial inhibitor (500ppm of sodium azide or mercuric chloride added immediately after sampling) i.e. no marked biodegradation occurred. 

Smdies of the thermal degradation of several aromatic acids have been reported. Phthalic acid (80), but not isophthalic acid (81) or terephthalic acid (82), decomposes via dehydration to its anhydride at 140-160 °C. However, (81) and (82) and benzoic acid are thermally stable below 200 °C. Dissociation constants of all 19 isomers of methyl-substimted benzoic acids (83) have been measured in methanol and DMSO. From the pA a values, the substiment effects of the methyl groups were calculated and tentatively divided into polar and steric effects. Also, in the case... 

Chemical/Physical. Hydrolyzes in water to o-phthalic acid (via the intermediate 2-ethyl-hexyl hydrogen phthalate) and 2-ethylhexyl alcohol (Kollig, 1993 Wolfe et al., 1980). Although no pH value was given, the reported hydrolysis rate constant under alkaline conditions is 1,400/M-yr (Ellington et al., 1993 Kollig, 1993). A second-order rate constant of 1.1 x 10 /M-sec was reported for the hydrolysis bis(2-ethylhexyl) phthalate at 30 °C and pH 8 (Wolfe et al., 1980). 

Biological. o-Phthalic acid was tentatively identified as the major degradation product of di-.n-octyl phthalate produced by the bacterium Serratia marcescens (Mathur and Rouatt, 1975). When di-.n-octyl phthalate was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum, no degradation was observed after 7 d. In a 21-d period, however, gradual adaptation did occur, resulting in 94 and 93% losses at concentrations of 5 and 10 mg/L, respectively (Tabak et ah, 1981). In the presence of suspended natural populations from unpolluted aquatic systems, the second-order microbial transformation rate constant determined in the laboratory was reported to be 3.7 + 0.6 x lO L/organism-h (Steen, 1991). 

Chemical/Physical. Reacts with water to form o-phthalic acid (Kollig, 1993 Windholz et al., 1983). Based on an observed rate constant of 7.9 x 10 /sec, the hydrolysis half-life is 88 sec (Hawkins, 1975). 

Values of rate constants in reaction (18 a) have been calculated (40) by means of this and similar treatments for a-ketoacids (44, 45), pyri-dinecarboxylic acids (46, 47), unsaturated acids (48, 49), phthalic acid (50), carbonyl compounds (51,52), iodobenzenes bearing ionisable groupings (53), etc. 

The pH of a 0.05 molar solution of acid potassium phthalate is 4.00 the first stage dissociation constant of phthalic acid is 1.3 X 10 what is pk2 for this acid ... 

The process of crystallization can be observed readily using phthalic acid. In the reference book The Handbook of Chemistry and Physics, in the table Physical Constants of Organic Compounds, the entry for phthalic acid gives the following solubiUty data (in grams of solute per 100 mL of solvent). The superscripts refer to temperature in °C ... 

Succinic acid (Ki = 6.66 X 10 K2 = X 10 ) behaves very much like phthalic acid although the first constant of succinic acid is only ten times greater than its second. 

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. 

Calculate the concentration of CSH4O4 (a) in a 0.010 M solution of H2CgH404, (b) in a solution which is 0.010 M with respect to H2C8H4O4 and 0.020 M with respect to HCl. The ionization constants for H2C8H4O4, phthalic acid, are... 

The charge vs. pH Curves 1 and 2 were calculated from alkalimetric titration curves of AUOs in the absence and presence of phthalic acid, respectively. The adsorption of total phthalic acid (formation of =AIXH and =AIX ) was determined analytically (Curve 3). Curve 4 was calculated from Curves 1 and 3 assuming that uncharged =AIXH only is formed. Curve 5 was calculated with the equilibrium constants given in Equation 24, the acidity constants of phthalic acid (—log Ko = 2.8, —log Kag = 4.9) (19). 

The first-order rate constant of the esterification of anhydrous phthalic acid catalyzed by nickel sulfates mounted on alumina and some other solid acids is shown in Table IV, together with the acidity of the catalysts measured by using p-dimethylaminoazobenezene as an indicator and the acidity calculated from the rate constants (cf. Section II). The catalytic activity correlates better with the acidity obtained by the latter method. The acidities measured by both methods coincide in the case of nickel sulfate, but do not in the case of silica-alumina. This is considered, according to Tarama et al., to be due to the fact that the Lewis acid sites which are assumed to be included in silica-alumina do not show catalytic activity. However, this might also be interpreted as due to the differences in acid strength and selectivity. 

Hamer WJ, Pinching GD and Acree SF, First dissociation constant of o-phthalic acid and related pH values of phthalate buffers from 0 to 60 , /. Res. Nat. Bur. Stand., 35, 539-564 (1945) Hamer WJ and Acree SF, /. Res. Nat. Bur. Stand., 35,381-416 (1945). NB Used electrochemical cell wiBiout liquid junction potentials detailed procedures were required to extrapolate ionic strengBi effects to zero. 

Figure 2.19. Dielectric constants of esters of phthalic acid and alcohols having different number of carhon atoms.

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