Decarboxylation dehydration, decarboxylative

D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates. 

At the other end of the reaction, deviations from idealized rate laws are attributed to secondary reactions such as degradations of acids, alcohols, and amines through decarboxylation, dehydration, and deamination, respectively. The step-growth polymers which have been most widely studied are simple... 

The principal steps in the mechanism of polyisoprene formation in plants are known and should help to improve the natural production of hydrocarbons. Mevalonic acid, a key intermediate derived from plant carbohydrate via acetylcoen2yme A, is transformed into isopentenyl pyrophosphate (IPP) via phosphorylation, dehydration, and decarboxylation (see Alkaloids). IPP then rearranges to dimethylaHyl pyrophosphate (DMAPP). DMAPP and... 

Heat. When heated, succinic acid loses water and forms an internal anhydride with a stable ring stmcture. Dehydration starts at 170°C and becomes rapid at 190—210°C (25). Further heating of succinic anhydride causes decarboxylation and the formation of the dilactone of gamma ketopimelic acid (26) (eq. 1). The same reaction takes place at lower temperatures in the presence of alkaU. 

In 1869 Berthelot- reported the production of styrene by dehydrogenation of ethylbenzene. This method is the basis of present day commercial methods. Over the year many other methods were developed, such as the decarboxylation of acids, dehydration of alcohols, pyrolysis of acetylene, pyrolysis of hydrocarbons and the chlorination and dehydrogenation of ethylbenzene." ... 

The method described is a modification of the procedure used by Ghosez to synthesize cinnamonitrile. 3-(2-Furyl)acrylo-nitrile has been prepared by catalytic condensation of furfural with acetonitrile in the vapor phase at 320°, by dehydration of the corresponding amide over phosphorus pentachloride, and by decarboxylation of 3-(2-furyl)-2-cyanoacrylic acid. ... 

The mechanism for the conversion of the A -oxide (94) to the o-methylaminophenylquinoxaline (96) involves an initial protonation of the A -oxide function. This enhances the electrophilic reactivity of the a-carbon atom which then effects an intramolecular electrophilic substitution at an ortho position of the anilide ring to give the spiro-lactam (98). Hydrolytic ring cleavage of (98) gives the acid (99), which undergoes ready dehydration and decarboxylation to (96), the availability of the cyclic transition state facilitating these processes. ... 

Condensation of an appropriately substituted phenylacetic acid with phthalic anhydride in the presence of sodium acetate leads to aldol-like reaction of the methylene group on the acid with the carbonyl on the anhydride. Dehydration followed by decarboxylation of the intermediate affords the methylenephthal-ides (12). Treatment of the phthalides with base affords directly the indandiones, probably via an intermediate formally derived from the keto-acid anion (13). The first agent of this class to be introduced was phenindandione (14) this was followed by anisindandione (1S) and chlorindandione (16). ... 

A thioamide of isonicotinic acid has also shown tuberculostatic activity in the clinic. The additional substitution on the pyridine ring precludes its preparation from simple starting materials. Reaction of ethyl methyl ketone with ethyl oxalate leads to the ester-diketone, 12 (shown as its enol). Condensation of this with cyanoacetamide gives the substituted pyridone, 13, which contains both the ethyl and carboxyl groups in the desired position. The nitrile group is then excised by means of decarboxylative hydrolysis. Treatment of the pyridone (14) with phosphorus oxychloride converts that compound (after exposure to ethanol to take the acid chloride to the ester) to the chloro-pyridine, 15. The halogen is then removed by catalytic reduction (16). The ester at the 4 position is converted to the desired functionality by successive conversion to the amide (17), dehydration to the nitrile (18), and finally addition of hydrogen sulfide. There is thus obtained ethionamide (19)... 

The amino acid leucine is biosynthesized from n-ketoisocaproate, which is itself prepared from -ketoisovalerate by a multistep route that involves (1) reaction with acetyl CoA, (2) hydrolysis, (3) dehydration, (4) hydration. (5) oxidation, and (6) decarboxylation. Show lhe steps in the transformation, and propose a mechanism for each. 

Ethyl 1-bromocyclohexanecarboxylate, when treated with magnesium in anhydrous ether-benzene with subsequent addition of cyclohexanone, yields ethyl l-(l-hydroxycyclohexyl)cyclo-hexanecarboxylate. Dehydration and saponification give rise to l-(l-cyclohexenyl)cyclohexanecarboxylic acid, which upon decarboxylation at 195° yields cyclohexylidenecyclohexane in 8% overall yield, m.p. 540.4 This olefin has also been prepared by the debromination of 1,1 -dibromobicyclohexyl with zinc in acetic acid. ... 

Together with the decarboxylation, dehydration of PPA takes place on heating. Examination of the decarboxylation of copolymers of acrylic and propynoic adds having blocks in their structure has revealed two interesting phenomena261 262. ... 

The reaction of olefin sulfation and its possibilities has been extensively studied [3-10] and it was used to produce alcohol sulfates. Dry distillation of spermaceti gives palmitic acid and cetene-1, which can be sulfated with sulfuric acid to give cetyl-2 sulfate [11]. Other surfactants were obtained from olefins produced from natural substances, such as alcohol sulfates by sulfation of olefins from decarboxylation of oleic acid [12], by sulfation of olefins made by dehydrating hydroabietyl alcohol, by direct sulfation of abietyl alcohol [13,14], or by sulfation of natural terpenes [15]. 

The trialkyltin alkoxides can often be prepared more conveniently by azeotropic dehydration of the appropriate bis(trialkyltin) oxide and alcohols, or by heating together the bis(trialkyltin) oxide and dialkyl carbonate (192). The latter reaction involves formation, and then decarboxylation, of the alkyl trialkyltin carbonate, e.g.,... 

Pyruvic acid is the simplest homologue of the a-keto acid, whose established procedures for synthesis are the dehydrative decarboxylation of tartaric acid and the hydrolysis of acetyl cyanide. On the other hand, vapor-phase contact oxidation of alkyl lactates to corresponding alkyl pyruvates using V2C - and MoOa-baseds mixed oxide catalysts has also been known [1-4]. Recently we found that pyruvic acid is obtained directly from a vapor-phase oxidative-dehydrogenation of lactic acid over iron phosphate catalysts with a P/Fe atomic ratio of 1.2 at a temperature around 230°C [5]. 

As for the reaction path from pyruvic acid to citraconic anhydride, it is considered that a condensation reaction first takes place by a reaction between an oxygen atom of carbonyl group and two hydrogn atoms of methyl group in another molecule, followed by oxidative decarboxylation to form citraconic acid. The produced citraconic acid is dehydrated under the reaction conditions used. The proposed reaction path is shown in Figure 7. 

If a-carboxylated oximes are treated with CDI[7] (A) or A V/-oxalyldiimidazole[8] (C) the dehydration proceeds with decarboxylation of the carboxy group. 

Metljylcoumarone has been prepared by the cyclization of ethyl a-phenoxyacetoacetate followed by hydrolysis and decarboxylation of the resulting ethyl 3-methylcoumarilate,3 4 by debromination and rearrangement of 3,4-dibromo-4-methyl-coumarin to 3-methylcoumarilic acid followed by decarboxylation,4-6 by cyclization of phenoxyacetone with concentrated sulfuric acid,6 and by treatment of 3-coumaranone with methyl-magnesium iodide followed by dehydration of the resulting car-binol.7... 

A bottle of analytical grade material exploded in laboratory storage at 25°C (undoubtedly from internal pressure of carbon dioxide). Pure material, protected from light and air, is only stable on a long term basis if kept refrigerated. Otherwise slow decomposition and decarboxylation occurs [1], possibly accelerated by enzymic catalysis from ingress of airborne yeasts. At ambient temperature, the acid dimerises and dehydrates to 2-oxo-4-carboxyvalerolactone [2],... 

One example will show the manifold types of reactions studied by Mok et al. (1989). Lactic acid decomposes in supercritical water to give acetaldehyde, which then reacts further it can also undergo dehydration to give acrylic acid, which is either hydrogenated to give propionic acid or decarboxylated to give ethene (Fig. 7.4). 

Several processes often occur in lipids, including oxidation, hydration, dehydration, decarboxylation, esterification, aromatization, hydrolysis, hydrogenation and polymerization. In fact, the chemistry of these materials can be affected, for example, by heat (anthropogenic transformations), humidity, pH, and microbial attacks. 

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