Homologization carboxylic acids

The paraffin wax is oxidized by air in a liquid phase process at 110-130°C. Catalysts for this radical reaction are cobalt or manganese salts [54]. The quality of the obtained mixture of homologous carboxylic acids is impaired by numerous byproducts such as aldehydes, ketones, lactones, esters, dicarboxylic acids, and other compounds. These are formed despite a partial conversion of the paraffin and necessitate an expensive workup of the reaction product [50,55]. 

Addition of a silyl substituent into a-position of the a-(benzotriazol-l-yl)alkyl ether brings additional possibilities. Thus, lithiation of silyl ether 770 followed by treatment with an aldehyde or ketone gives unstable P-hydroxy-a-silyl-a-(benzotriazol-l-yl)alkyl ether 771 that spontaneously eliminates silanol to give vinyl ether 772 (Scheme 121). Treatment with ZnBr2 followed by hydrolysis with a diluted acid removes both the benzotriazolyl and the methyl groups to furnish carboxylic acid 773. In this way, in a simple manner, aldehydes and ketones are converted to one-carbon homologated carboxylic acid <1996S1425>. 

The use of copper as a catalyst in carbenoid transfer has its roots in the Amdt-Eistert reaction, Eq. 1 (3). Although the original 1935 paper describes the Wolff rearrangement of a-diazo ketones to homologous carboxylic acids using silver, the authors mention that copper may be substituted in this reaction. In 1952, Yates (4) demonstrated that copper bronze induces insertion of diazo compounds into the X-H bond of alcohols, amines, and phenols without rearrangement, Eq. 2. Yates proposal of a distinct metal carbenoid intermediate formed the basis of the currently accepted mechanistic construct for the cyclopropanation reaction using diazo compounds. 

Treatment of the ketene with water would give the corresponding homologated carboxylic acid. 

Only small amounts of side products are formed. The purity of the acid is mostly greater than 98%, the major side product (up to 2%) is the lower homologous carboxylic acid. 

The reagent is generally useful for conversion of aromatic, heteroaromatic, and aliphatic aldehydes into the homologous carboxylic acid in satisfactory yield.1... 

The Arndt-Eistert Synthesis allows the formation of homologated carboxylic acids or their derivatives by reaction of the activated carboxylic acids with diazomethane and subsequent Wolff-Rearrangement of the intermediate diazoketones in the presence of nucleophiles such as water, alcohols, or amines. 

Barbier-Wieland degradation. Stepwise carboxylic acid degradation of aliphatic acids (particularly in sterol side chains) to the next lower homo log. The ester is converted to a tertiary alcohol that is dehydrated with acetic anhydride, and the olefin oxidized with chromic acid to a lower homologous carboxylic acid. 

Homologations. Hydroformylation of S- and O-containing alkenes is mediated by Rh4(CO)i2. Homologous carboxylic acids and derivatives (esters, amides) are obtained from allyl phosphates. ... 

The preceding discussion emphasizes the applicability of Eq. (6-6) for adsorption onto polar adsorbents, particularly adsorbent samples deactivated by varying amounts of water. However, the derivation of Eq. (6-6) does not preclude its application to nonpolar adsorbents. Claesson has in fact observed 14) the existence of a similar relationship for adsorption onto various charcoals. For the homologous carboxylic acids as samples and ethanol as solvent, the Langmuir isotherm [Eq. (3.6-)] was found to describe the adsorption of each acid. The derived values of the Langmuir coefficient k [or K° in Eq. (3-6)] could be expressed as a function of the number n of carbon atoms in the sample molecule ... 

Equations (10-4) and (10-4a) predict a linear dependence of logX or R i on n for samples of the general class X-i . Some experimental examples of this relationship are shown in Fig. 10-1. These include the elution of the unsubstituted aromatic hydrocarbons of carbon number n from alumina (a) and Florisil (f>), the equilibrium adsorption of the homologous carboxylic acids (C Fl2 nCOOH) on charcoalt (c), and the thin-layer separation of some methyl ester-substituted porphyrins (porph... 

The Wolff rearrangement of a-diazocarbonyl compounds (8.58, R = H, alkyl, aryl, OR) has great synthetic importance because in most cases the ketenes formed react smoothly with water, alcohols, and amines (Scheme 8-34). An early application that still has considerable importance is the homologization of carboxylic acids (Arndt-Eistert reaction Arndt and Eistert, 1935). As shown in Scheme 8-34, the reaction starts from the chloride of the acid RCOOH, which leads to an a-diazo ketone with diazomethane (R = H), followed by the Wolff rearrangement and the hydrolysis of the ketene intermediate to give the homologous carboxylic acid (8.59, R =H). In alcohols and amines esters (8.60) and amides (8.61, R = H), respectively. 

On the other hand, from a qualitative standpoint, this value has always been, quite justifiably, linked to quality. Indeed, when an enologist tastes a wine and decides there is excessive volatile acidity, this derogatory assessment has a negative effect on the wine s value. This organoleptic characteristic is related to an abnormally high concentration of acetic acid, in particular, as well as a few homologous carboxylic acids. These compounds are distilled when wine is evaporated. Those which, on the contrary, remain in the residue constitute fixed acidity. 

Triethylamine sec-butyl chloroformate Modified Arndt-Eistert synthesis Homologous carboxylic acid esters from carboxylic acids... 

An electrosynthetic procedure has been described for converting alkyl halides into the homologous carboxylic acids. Carbon dioxide... 

Similar reactions, but using nitroalkenes as traps, lead to the corresponding a-pyridylthio nitroalkanes, which are useful as precursors to the one-carbon homologated carboxylic acids, aldehydes, or the related ketones, by starting with an a-substituted nitroalkene (eq 14). ... 

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