Acid derivatives, pyrolytic reactions

Another example of this is the loss of acetic acid when delphinine is heated in hydrogen at 200-215°. Just as aconitine is so converted into pyraconitine so delphinine yields pyrodelphinine, C3 H4 0,N, m.p. 208-212°, and similarly a-oxodelphinine, C33H430j qN, under like treatment loses acetic acid and yields pyro-a-oxodelphinine, C3 H3gOgN, which crystallises from methyl alcohol in needles, m.p. 248-250°, after sintering at 238°. This, on hydrogenation, forms a hexahydro-derivative, m.p. 183-5°, presumably by saturation of the benzoyl radical, which therefore leaves unexplained the mechanism by which acetic acid is lost in this pyrolytic reaction (c/. pyropseudaconitine, p. 683). 

Quaternary ammonium salts of fatty acids are converted to methyl ester derivatives pyrolytically in the injection port of a gas chromatograph. Of a number of reagents which have been described for the purpose, it appears that trimethylsulfonium hydroxide is the most powerful and exhibits fewer side reactions it can be used for the simultaneous transesterification of lipids and esterification of free acids [144]. 

F. derives de cyclodextrine Aim of derivatization is increased versatility by increasing the hydrophilic character of the outer surface area. This is accomplished with substituents such as sulfuric acid esters and alkyl, hydro-xyalkyl, carboxymethyl, aminoalkyl ethers formation of carboxyl groups by glycolic oxidation formation of branched c. with glucose or oligosaccharide side chains by pyrolytic reactions. Derivatization is mostly performed with P-cyclo-dextrin. Solubilities depend on DS as well as on the nature of the substituent groups levels up to 60% have been reached. In such cases, the viscos-... 

The derivative-forming process in pyrolytic alkylation involves two sequential reactions deprotonation of the acidic substrate in aqueous solution by the strongly basic tetra-alkylammonium ion and the thermal decomposition of the quaternary M-alkylammonium salt formed to give a tertiary amine and alkyl derivative. For some weak acids both processes may occur virtually simultaneously in the injector oven of the gas chromatograph. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

Retro-Diels-Alder reactions can be used to regenerate dienes or alkenes from Diels-Alder protected cyclohexene derivatives under pyrolytic conditions144. Most of the synthetic utility of this reaction comes from releasing the alkene by diene-deprotection. However, tetralin undergoes cycloreversion via the retro-Diels-Alder pathway to generate o-quinodimethane under laser photolysis (equation 89)145. A precursor of lysergic acid has been obtained by deprotection of the conjugated double bond and intramolecular Diels Alder reaction (equation 90)146. 

Tetrathianes. (1) Oxidative dimerization of a,a-disuhstituted alkanedithioic acid dianions (Scheme 38) or 1,1-dithiols (Equation 17) - very limited examples and a-monosuhstituted alkanedithioic acids decompose (2) reductive or pyrolytic dimerization of gi OT-disulfenyl dichlorides (Equation 18) - only malonate-derived examples (3) reaction of a-chloro sulfenyl chlorides with sodium trithiocarhonate (Equation 19) - only malonate-derived examples (4) sodium thiophenoxide-catalyzed reaction of thioketones with elemental sulfur (5) reaction of benzo-furan-3(2//)-one with S2CI2" (6) UV irradiation of a CS2 solution of a diazirine (7) reaction of a 2,2,4-trisubstituted-1,3-dithietane with Oxone (Scheme 54)". Method (4) is the most convenient and general of these. 

In the presence of a Lewis acid, silyl enol ethers can be alkylated with reactive secondary halides, such as substituted benzyl halides, and with chloromethylphenyl sulfide (ClCH2SPh), an activated primary halide. Thus, reaction of the benzyl chloride 10 in the presence of zinc bromide with the trimethylsilyl enol ether derived from mesityl oxide allowed a short and efficient route to the sesquiterpene ( )-ar-turmerone (1.22). Reaction of ClCH2SPh with the trimethylsilyl enol ethers of lactones in the presence of zinc bromide, followed by 5-oxidation and pyrolytic ehmination of the resulting sulfoxide (see Section 2.2), provides a good route to the a-methylene lactone unit common in many cytotoxic sesquiterpenes (1.23). Desulfurization with Raney nickel, instead of oxidation and elimination, affords the a-methyl (or a-alkyl starting with RCH(Cl)SPh) derivatives. ... 

As alluded (vide supra), some confusion may arise with respect to this named reaction as there is reference in the literature to an alternative reaction with the same name. The Bradsher reaction forms aromatic rings but via an acid-catalyzed Friedel-Crafts-like process. Thus diaryl-methanes having a carbonyl group in the ortho position can undergo a cyclodehydration reaction to generate the corresponding anthracene derivatives. In this respect, the Bradsher reaction is related to the Elbs reaction, which involves the pyrolytic cyclization of diaryl ketones 6 having an ortho methyl or methylene substituent for the formation of polycyclic aromatics 7. 

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