Estimations acetyl derivatives

A. Gr. Perkin s Acetyl method. (Arur. Chem. Sot-., 1904, 20, 171). The method consists in hydiolysing the acetyl derivative in presence of alcohol and di.stilling off the ethyl acetate and then estimating the quantity by hydrolysis. 

The chain-length of this arabinose-free xylan was shown by methyla-tion and estimation of the hydrolysis products, using chromatographic methods, to be 35 3 D-xylose units. Osmotic pressure and viscosity measurements indicated that the degree of polymerization of the methylated and acetylated derivatives was about 70-90 xylose residues, and a structure for the xylan involving branching was confirmed. 

On the other hand, the presence of hydroxyl groups in the tannin molecules can promote interactions by adsorption on the gel or intermolecular linkage by hydrogen bonding, which would lead to incorrect estimation of the MW. These phenomena can be minimized by the use of very polar mobile phases, such as dimethylsulfoxide (DMSO), dimethylformamide (DMF), or tetrahydrofuran (THE) [68-70]. Another procedure is to protect the hydroxyl groups as acetyl derivatives, methyl derivatives, or silyl derivatives [71]. 

CgHs-N C CHs+CHaC OH In the above equations, it should be noted that acetyl chloride does not convert aniline completely into the acetyl derivative since the by-product, aniline hydrochloride, is formed and this does not act readily with the reagent. On the other hand, with acetic anhydride the amine is converted quantitatively into the acyl derivative and therefore this latter reagent is of more importance in connection with the preparation of derivatives. It is also of value in quantitative estimations of the amine group, the excess of acetic acid which remains after the reaction being determined volumetrically. Benzoyl chloride, benzenesulfonyl chloride, and other acyl halides that may be used in aqueous solution may also convert the amine completely into an acyl derivative for the reason that they are usually used in the presence of alkali which will combine with the hydrochloric acid generated in the reaction. When benzoyl chloride is used, a small amount of benzoic acid may be formed, due to the following side-reaction ... 

Partial rate factors may be used to estimate product distributions in disubstituted benzene derivatives The reactivity of a particular position in o bromotoluene for example is given by the product of the partial rate factors for the corresponding position in toluene and bromobenzene On the basis of the partial rate factor data given here for Fnedel-Crafts acylation predict the major product of the reaction of o bromotoluene with acetyl chlonde and aluminum chloride... 

In the case of a diketone (e.g., 3-tosyloxypentane-2,4-dione), the formation of 5-acetyl-4-methyl-2-aryl-l,3-thiazole derivatives can be realized in very good yields (86-89%) (Scheme 7). All these experiments where performed in a Sears Kenmore unmodified household microwave oven (990 W) equipped with a turntable. The average bulk temperature was estimated by inserting a thermometer in the alumina bath housing the reaction vessel. 

Neomycin has been separated from mixtures of other aminoglycoside antibiotics containing the 2-deoxystreptamine moiety as both the pertrimethylsilyl derivative and the N-trifluoro-acetyl pertrimethylsilyl derivative using a column of 0.75% 0V-1 on Gas Chrom q240. The procedure may be used to estimate the number of sugar moieties bound in the antibiotic as a close relationship exists between the number of rings and the retention time. 

Hammer, W. M., and Brodie, B. B., Application of isotope derivative technique to assay of secondary amines estimation of desipramine by acetylation with H -acetio anhydride. J. Pharmacol. Exp. Ther. 157, 503-508 (1967). 

The chapter is divided into three sections the first part is concerned with the derivation of 3D-LogP descriptor and the selection of suitable parameters for the computation of the MLP values. This study was performed on a set of rigid molecules in order, at least initially, to avoid the issue of conformation-dependence. In the second part, both the information content and conformational sensitivity of the 3D-LogP description was established using a set of flexible acetylated amino acids and dipeptides. This initial work was carried out using log P as the property to be estimated/predicted. However, it should be made clear that, while the 3D-LogP descriptor can be used for the prediction of log P, this was not the primary intention behind its the development. Rather, as previously indicated, the rationale for this work was the development of a conformationally sensitive but alignment-free lipophilicity descriptor for use in QSAR model development. The use of log P as the property to be estimated/predicted enables one to establish the extent of information loss, if any, in the process used to transform the results of MLP calculations into a descriptor suitable for use in QSAR analyses. 

It is clear (23) that three products result from reactions of acetoxy radical pairs within the solvent cage acetyl peroxide (estimated at 38% ), methyl acetate (12.4% ), and ethane (2.9% ). The implied near equality of rates for decarboxylation of the acetoxy radicals and diffusion from the cage has been given quantitative expression in work of Braun, Rajben-bach, and Eirich (2). These workers studied the variation in the amounts of ethane and methyl acetate formed from acetyl peroxide as a function of solvent viscosity, and they derived a rate constant for the decarboxylation of acetoxy radical at 60°C. of 1.6 X 109 sec."1. 

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