Labeled benzoic acid

Then the tropylium bromide was subjected to a Grignard reaction and the product oxidized to give a labeled benzoic acid. Thus, one had... 

The specific activity of the labeled benzoic acid was found to be one-seventh that of the initial labeled diazomethane, thus showing the equivalence of the seven carbon atoms of the tropylium ring. 

This sequence yields 14C-labeled benzyl alcohol, which can be oxidized to C-labeled benzoic acid. 

The decarboxylation of radio-labelled benzoic acid, the labelled... 

M. L. Bianconi and S. Schreier, ESR study of membrane partitioning, orientation, and membrane-modulated alkaline hydrolysis of a spin-labeled benzoic acid ester, J. Phys. Chem. 95, 2483-2486(1991). 

In C-carbonyl-labelled benzoic acid and benzophenone, Vujanic et reported V( C, C) couplings that depend on solvent. They were rationalized in the former as originating in changes in the intramolecular hydrogen bond in solution, and in the latter in changes in the ring planes dihedral angle. 

In aprotic solvents, the allylic carbonium ion and carboxylic acid molecule produced by acid-catalyzed heterolysis of an allylic ester may recombine to form the starting material and its allylic isomer. Kinetic studies show that a-phenylallyl p-nitrobenzoate undergoes concurrent uncatalyzed and p-nitro-benzoic acid-catalyzed isomerization to cinnamyl benzoate in chlorobenzene solutions containing p-nitrobenzoic acid . Similarly, benzoic acid catalyzes the isomerization of a-phenylallyl benzoate in chlorobenzene. When this reaction was carried out using 0-labeled benzoic acid, appeared in both the starting material and its allylic isomer under the conditions used, only about a quarter of the isomerization reaction is intramolecular. 

Intramolecular distributions of tritium, examples of which can be seen in Fig. 2, have been investigated by a number of authors. No cases have been found in which the distribution is truly random in the parent molecule (cf. glucose, alanine, and iraws-cinnamic acid, Fig. 2). Cases in which the replacement of a specific group by tritium might be expected to lead to a specifically labeled molecule have also not been found (cf. labeled benzoic acid from p-hydroxybenzoic acid, Fig. 2). 

Initially a large variability in the relative response factors of the methyl derivative of MX to that of isotopi-cally labeled benzoic acid was observed as a function of relative concentrations, indicating a nonlinear response of the analyte relative to that of the VIS. This nonlinear behavior was shown (Charles 1992) to not arise from competition between MX and the benzoic acid standard in the derivatization reaction (the methylating agent was in very large excess), but rather from a peculiarity of the SIM... 

Labeled benzoic acid was reacted with DBU and DMC at 90°C. The study indicated that an approximately 1 1 mixture of labeled methyl benzoates was obtained (Scheme 20.9). 

When benzoic acid is allowed to stand in water enriched in isotopic label becomes incorporated into the benzoic acid The reaction is cat alyzed by acids Suggest an explanation for this observation... 

The two OH groups m the tetrahedral intermediate are equivalent and so either the labeled or the unlabeled one can be lost when the tetrahedral intermediate reverts to ethyl benzoate Both are retained when the tetrahedral intermediate goes on to form benzoic acid... 

Water labeled with 0 adds to benzoic acid to give the tetrahedral intermediate shown This intermediate can lose unlabeled H2O to give benzoic acid containing 0... 

A cleai-cut answer was provided by Irving Roberts and Harold C. Urey of Columbia University in 1938. They prepared methanol that had been enriched in the rnass-18 isotope of oxygen. When this sfflnple of methanol was esterified with benzoic acid, the methyl benzoate product contained all the label that was originally present in the methanol. 

Evidence in support of the mechanism shown in figure 21.4 comes from isotope-labeling experiments. When 180-labeled methanol reacts with benzoic acid, the methyl benzoate produced is found to be l80-labeled but the water produced is uniabeled. Thus, it is the C-OH bond of the carboxylic acid that is broken during the reaction rather than the CO—H bond and the RO-H bond of the alcohol that is broken rather than the R-OH bond. 

Hydroxyphenylpyruvic acid plays an important role in the biogenesis of compounds with a phenylpropane skeleton, and it has been used as substrate in several enzyme studies. Published procedures for its preparation are unsatisfactory in many ways. The alkaline hydrolysis of the azlactone of a-bcnzoylamino- -acetoxycinnamic acid 7 makes necessary a tedious separation of the resulting benzoic acid, and the yield is only 34% based on -hydroxybenzaldehyde. The hydrolysis of 5- ( -hydroxybenzal)-3-phenylhydantoin 9 requires a separation of phenylurea. Finally, the two-step cleavage of the azlactone of a-acetamino- -acetoxycinnamic acid 8 does not proceed easily, and impure products are obtained. In applying this procedure to the synthesis of a carboxyl-labeled -hydroxyphenylpyruvic acid, the overall yield was only 9%.u It must be kept in mind that any prolonged isolation procedure will cause some decomposition of this sensitive compound. 

K. Haider and J. P. Martin, Decomposition of specifically carbon-14 labeled benzoic and cinnamic acid derivatives in soil. Soil Sci. Soc. Am. Proc. 39 651 (1975). 

Proteases are enzymes that break peptide bonds in proteins. As such they lend themselves to a variety of homogeneous assay techniques. Most employ labeling both ends of the substrate with a different tag, and looking for the appearance (disappearance) of the signal generated in the intact substrate (product). As an example, for a fluorescence quench assay, the N-terminal of a peptide is labeled with DNP and the C-terminal with MCA. As such, the peptide is fluorescently silent since the fluorescence from DNP is quenched by absorption by the MCA. Another very popular donor/acceptor pair is EDANS 5-[(2-aminoethyl)amino] naphthalene-1-sulfonic acid and DABCYL 4-(4-dimethylaminophenylazo)benzoic acid) (a sulfonyl derivative (DABSYL) [27], Upon peptide cleavage, the two products diffuse, and due to a lack of proximity, the fluorescence increases. 

The Hammett equation is the best-known and most widely studied of the various linear free energy relations for correlating reaction rate and equilibrium constant data. It was first proposed to correlate the rate constants and equilibrium constants for the side chain reactions of para and meta substituted benzene derivatives. Hammett (37-39) noted that for a large number of reactions of these compounds plots of log k (or log K) for one reaction versus log k (or log K) for a second reaction of the corresponding member of a series of such derivatives was reasonably linear. Figure 7.5 is a plot of this type involving the ionization constants for phenylacetic acid derivatives and for benzoic acid derivatives. The point labeled p-Cl has for its ordinate log Ka for p-chlorophenylacetic acid and for its abscissa log Ka for p-chloroben-zoic acid. The points approximate a straight line, which can be expressed as... 

Line 2. dracylic acid. What a synonym Label your benzoic acid bottles this way and no one will ever borrow your benzoic acid again. 

Soil. In unsterilized soils, 58% of C-labeled sulfometuron-methyl degraded after 24 wk. Metabolites identified were 2,3-dihydro-3-oxobenzisosulfonazole (saccharin), methyl-2-(amino-sulfonyl) benzoate, 2-aminosulfonyl benzoic acid, 2-(((aminocarbonyl)amino)sulfonyl) benzoate, and [ C]carbon dioxide. The rate of degradation in aerobic soils was primarily dependent upon pH and soil type (Anderson and Dulka, 1985). The reported half-life in soil was approximately 4 wk (Hartley and Kidd, 1987). 

The absorption (following administration by oral, intramuscular and intravenous routes), distribution and elimination of the drug has been studied by radiotracer techniques in rats and rabbits [283, 284]. The substituted benzoic acid was labelled with and the alkanolamine remnant with Almost all radioactivity was recovered from the urine even after oral administration. 

Once lignin has been degraded into monomeric products, the degradation of the individual aromatic monomers proceeds quite rapidly. Haider and Martin (53) have shown that C-labeled benzoic and cinnamic acids and their derivatives can be aerobically mineralized in the first two weeks, and some of the compounds had over 90% of their carbon converted to CO2 in one week. 

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