4- Isopropylbenzoic acid

Li added during 3 min. at 40° to a stirred suspension of 2-isopropylbenzoic acid in liq. NH3 and water, NH3 evaporated, and acidified with aq. 20%-HCl 2-iso-propyl-2,5-cyclohexadiene-l-carboxylic acid. Y 81%. - Isomeric 1,5-cyclohexa-diene-l-carboxylic acids may be obtained in the presence of ethanol instead of water, which is a more powerful proton donor. F. e. s. H. van Bekkum et al., R. 90,137 (1971). 

A quantum-chemical study of the mechanism of the condensation reaction between propanoic acid and aniline has been made. The mechanism of proton-transfer reactions of 3,5-dinitrosalicylic acid (41) has been the subject of a review (50 references). A successful correlation has been obtained between dissociation of a variety of acids in different solvents and quantum self-similarity measures of the CO2H fragment. The substituent effects of the isopropyl group in 2- (42), 3- (43), and 4-isopropylbenzoic acid (44) have been evaluated from their enthalpies of formation, gas-phase acidities, acidities in MeOH and in DMSO, and their IR spectra in tetrachloromethane. Particular attention was given to the influence of variable conformation on the observed steric effect. In contrast to 2-r-butylbenzoic acid and similarly to 2-methylbenzoic acid, 2-isopropylbenzoic acid exists in two planar conformations (42a,b) in equilibrium. Owing to this conformational freedom, the... 

An additional curious feature of alkylaromatic oxidation is that, under conditions where the initial attack involves electron transfer, the relative rate of attack on different alkyl groups attached to the same aromatic ring is quite different from that observed in alkane oxidation. For example, the oxidation of -cymene can lead to high yields of -isopropylbenzoic acid (2,205,297,298). 

As indicated by metastable ion studies of isopropylbenzoic acids, [202] the formation of the ion at m/z 90 should be described as a two-step process, i.e., the product rather is [M-OH-CHO] than [M-HCOOH]. This would add yet another example to the list of violations of the even-electron rule (Chap. 6.1.3). 

Example Examination of the mass spectrum of isopropylbenzoic acid reveals that the molecular ion, m/z 164, as well as the [M-CHs] ion, m/z 149, eliminate H2O via ortho elimination yielding fragment ions at m/z 146 and 131, respectively (Fig. 6.47). [202] The [M-CH3-H20] ion, a homologue of the benzoyl ion, decomposes further by loss of CO, thereby creating a fragment that overall corresponds to [M-CHs-HCOOH]-, m/z 103. 

Fig. 6.47. El mass spectrum of isopropylbenzoic acid. Spectrum used by permission of NIST. NIST 2002.

Similarly, the cobalt acetate-catalyzed autoxidation of p-cymene afforded mainly p-isopropylbenzoic acid,243,244 246 derived from selective oxidation of the methyl group. Manganese acetate, on the other hand, was involved in a catalyzed autoxidation,... 

Tyrosinase inhibitors prevent browning in foodbecause they inhibit the oxidation caused by the enzyme tyrosinase. Cuminaldehyde is identified as a potent mushroom tyrosinase monophenol monooxygenase inhibitor from cumin seeds, ft inhibits the oxidation of L-3,4-dihydroxyphenylalanine (l-DOPA) by mushroom tyrosinase with an ID50 of 7.7g/ml (0.05 mM). Its oxidized analogue, cumic acid (p-isopropylbenzoic acid), also inhibits this oxidation with an 1D50 of 43g/ml (0.26mM). These two inhibitors affect mushroom tyrosinase activity in different ways (Kubo and Kinst-Hori, 1998). 

Hydrogen peroxide is prone to decomposition under alkaline conditions. To counteract this problem, stabilizers, which may be used under strongly alkaline conditions, can be employed. The oxidation of 4-isopropylbenzaldehyde to 4-isopropylbenzoic acid requires significantly less hydrogen peroxide when the appropriate stabilizer is used (Figure 3.44). 

Cl 1HI403 2-hydroxy-3-methyl-6-isopropylbenzoic acid 4389-53-1 22.07 1.0913 2 22402 Cl1 HI 60 2-tert-butyl-5-methylphenol 88-60-8 80.00 0.9220 1... 

Cl 1 HI 403 2-hydroxy-6-methyl-3-isopropylbenzoic acid 548-51-6 22.07 1.0913 2 22403 C11H160 2-tert-butyl-6-methylphenol 2219-82-1 80.00 0.9240 1... 

The partial oxidation of polyalkylated aromatic compounds is also observed. o-Xylene is oxidized to o-toluic acid by heating with ozone and oxygen at 115-120 °C in the presence of cobalt acetate in acetic acid (yield 77%) [68] or by refluxing with dilute nitric acid (1 2) (yield 53-55%) [463]. In p-cymene (p-isopropylbenzene), the isopropyl group is oxidized in preference to the methyl group to give a 51% yield of p-toluic acid on refluxing with dilute nitric acid (1 36) [464]. On the contrary, biochemical oxidation with Nocardia strain 107-332 converts p-cymene into p-isopropylbenzoic acid [1071]. 

Hydroxy-6-niethyl-3-isopropylbenzoic acid 2-Hydroxy-3-methyl-6-isopropyl-2-cyclohexen-1-one... 

Isopropylbenzoic acid ( CioHta e ) 4-DinethylaminobenzoIc acid ( CjHnOjN )... 

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