A-p-Nitrobenzoates

The products of peracid oxidation of limonene have also been re-examined. Wylde and Teulon have shown that the best method for making pure cis-or trans- limonene 1,2-epoxides, a mixture of which is obtained by direct peracid oxidation in chlorinated hydrocarbon solvents, is to treat this mixture with hydrogen chloride in ether, when the two diaxial chlorohydrins (122) and (123) are obtained with practically no equatorially substituted isomers. Of these two isomers only (122) forms a p-nitrobenzoate, allowing (123) to be distilled from the residue. Treatment of the nitrobenzoate of (122) with methanolic potassium hydroxide now leads to the c/s-epoxide (120) similar treatment of... 

Fig. 1. Intensity of two Raman bands of a p-nitrobenzoic acid (PNBA) monolayer, adsorbed in the multilayer structure shown in the inset, vs. a polymethylmethacrylate (PMMA) spacer of thickness d. Open symbols, 1100cm 1 band closed symbols 1597cm-1 band. (Reproduced with permission from ref. 11.)...

The ee of the recovered allylic alcohol 10 was obtained by first converting the alcohol group to a p-nitrobenzoate [61]. 

Our first synthesis of lactones via allylboration involved the protection of homoallylic alcohols as a p-nitrobenzoate ester, followed by hydroboration with chloroborane and oxidation of the intermediate with CrOa in acetic acid. Deprotection under basic conditions provided the lactones in very high yields with the same enantiomeric excesses as the starting homoallyl alcohols (Scheme 3) (6). 

Thionyl chloride method. Mix 100 g. of pure p-nitrobenzoic acid and 125 g. (77 ml.) (1) of redistilled thionyl chloride in a 500 ml. round-bottomed flask. Fit the flask with a double surface reflux condenser carrying a calcium chloride (or cottou wool) guard tube and connect the latter to an absorption device e.g.. Fig. II, 8, c). Heat the flask on a... 

A large excess of thionyl chloride is recommended in order to avoid the format tion of p-nitrobenzoic anhydride (see Note 1 to Section IV,185). 

Method 2. Ethyl p-nitrobenzoate. Place 21 g. of p-nitrobenzoic acid (Section IV,154), 11-5 g. of absolute ethyl alcohol, 3 8 g. of concentrated sulphuric acid, and 30 ml. of sodium-dried A.R. benzene in a 250 ml. round-bottomed flask, fit a reflux condenser, and heat the mixture under reflux for 16 hours. Add 50 ml. of ether to the cold reaction mixture, wash the extract successively with sodium bicarbonate soiution and water, dry with anhydrous magnesium sulphate or calcium chloride, and distil off the solvent on a water bath. Remove the last traces of benzene either by heating in an open evaporating dish on a water bath or in a bath at 100-110°. The residual ethyl p-nitrobenzoate (21 g.) solidifies completely on cooling and melts at 56°. 

Determination of melting points (a-naphthylamine, a-naphthol, benzoic acid, succinic acid and p-nitrobenzoic acid). Use the apparatus shown in Fig. II, 10, 2, a. Construction of calibration curve for thermometer. Determination of m.p. of unknown compound. 

A related problem concerns the synthesis of p nitrobenzoic acid Here two meta directing substituents are para to each other This compound has been prepared from toluene according to the procedure shown... 

Hydrolysis of either A or B yields RNHCH2CH2OH and p nitrobenzoic acid Suggest a reason able structure for compound B and demonstrate your understanding of the mechanism of this reaction by wnting the structure of the key intermediate in the conversion of compound A to com pound B... 

Hydrolysis of the ester is achieved by refluxing in aqueous N or 2N NaOH solution until the insoluble ester dissolves. The solution is then cooled, and the alcohol is extracted into a suitable solvent, e.g. ether, toluene or alcohol-free chloroform. The extract is dried (CaS04, MgS04) and distilled, then fractionally distilled if liquid or recrystallised if solid. (The p-nitrobenzoic acid can be recovered by acidification of the aqueous layer.) In most cases where the alcohol to be purified can be readily extracted fi-om ethanol, the hydrolysis of the ester is best achieved with N or 2N ethanolic NaOH or 85% aqueous ethanolic N NaOH. The former is prepared by dissolving the necessary alkali in a minimum volume of water and diluting with absolute alcohol. The ethanolic solution is refluxed for one to two hours and hydrolysis is complete when an aliquot gives a clear solution on dilution with four or five times its volume of water. The bulk of the ethanol is distilled off and the residue is... 

The cause of this effect has been called B-strain (back-strain), and in this exanqjle only a modest rate enhancement is observed. As the size of the groups is increased, the effect on rate becomes larger. When all three of the groups in the above example are t-butyl, the solvolysis occurs 13,500 times faster than in the case of t-butyl p-nitrobenzoate. ... 

Another feature of systems that are subject to B-strain is their reluctance to form strained substitution products. The cationic intermediates usually escape to elimination products in preference to capture by a nucleophile. Rearrangements are also common. 2-Methyl-2-adamantyl p-nitrobenzoate gives 82% methyleneadamantane by elimination and 18% 2-methyl-2-adamantanol by substitution in aqueous acetone. Elimination accounts for 95% of the product from 2-neopentyl-2-adaman l p-nitrobenzoate. The major product (83%) from 2-r-butyl-2-adamantyl p-nitrobenzoate is the rearranged alkene 5. 

In aqueous dioxane, the endo-anti isomer gave a product mixture consistent of alcohol N and the corresponding ester (derived from capture of the leaving group p-nitrobenzoate). The other isomers gave much more complex product mixtures which were not completely characterized. Explain the trend in rates and discuss the structural reason for the stereochemical course of the reaction in the case of the endo-anti isomer. 

Recently, in extending the reaction to aliphatic glycols, Ghera observed that p-nitrobenzoate esters gave better results than acetates, and that zinc acetate could be substituted for activated zinc. He has proposed that the rearrangement is a heterogeneous catalytic process, with the zinc acting as a Lewis acid ... 

This phenomenon is not possible in p-nitrobenzoic acid hence, p-nitrophenol is a stronger acid with respect to p-nitrobenzoic acid than is expected on the basis of a comparison of substituents in which this resonance delocalization is not an important factor. It was, therefore, recommended that Op = 1.27 be used for p-nitro derivatives of phenols and anilines, rather than the Op = 0.78 given in Table 7-10. These enhanced sigma constants, symbolized a, apply primarily to electron-withdrawing groups in reactions aided by low electron density at the reaction site. 

Sc(OTf)3, AcOH, p-nitrobenzoic anhydride or Sc(OTf)3, AC2O, 66- >95% yield. The lower yields are obtained with allylic alcohols propargylic alcohols give higher yields. Phenols are effectively acylated with this catalyst, but at a much slower rate than simple aliphatic alco-hols. The method was shown to be superior to most other methods for macrolactonization with minimum diolide formation. 

In extending this direct method of synthesis, we next investigated the possibility of preparing similarly constituted halides from 2-deoxy-D-arabino-hexose (2-deoxy-D-glucose) (21). The hexose was subjected to a partial anomerization procedure described by Bergmann and co-workers (1). The solid material obtained by this procedure is a mixture of the anomeric forms of 2-deoxy-D-arabino-hexose low temperature p-nitro-benzoylation of the latter in pyridine resulted in a mixture of crystalline, anomeric tetrakis-p-nitrobenzoates in a ratio of approximately 1 1. They were readily separable by fractional recrystallization, and treatment of either with an excess of hydrogen bromide in dichloromethane, or with... 

Jaffe (1953)52 showed that while many rate or equilibrium data conform well to the Hammett equation (as indicated by the correlation coefficient), many such data are outside the scope of the equation in its original form and mode of application. Deviations are commonly shown by para-substituents with considerable + Rot — R effect53. Hammett himself found that p-NOz (+ R) showed deviations in the correlation of reactions of anilines or phenols. The deviations were systematic in that a a value of ca. 1.27 seemed to apply, compared with 0.78 based on the ionization of p-nitrobenzoic acid. Other examples were soon discovered and it became conventional to treat them similarly in terms of a duality of substituent constants . 

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