Acetylenic acids allenic acid

Acetylene is sufficiently acidic to allow application of the gas-phase proton transfer equilibrium method described in equation l7. For ethylene, the equilibrium constant was determined from the kinetics of reaction in both directions with NH2-8. Since the acidity of ammonia is known accurately, that of ethylene can be determined. This method actually gives A f/ acid at the temperature of the measurement. Use of known entropies allows the calculation of A//ac d from AG = AH — TAS. The value of A//acij found for ethylene is 409.4 0.6 kcal mol 1. But hydrocarbons in general, and ethylene in particular, are so weakly acidic that such equilibria are generally not observable. From net proton transfers that are observed it is possible sometimes to put limits on the acidity range. Thus, ethylene is not deprotonated by hydroxide ion whereas allene and propene are9 consequently, ethylene is less acidic than water and allene and propene (undoubtedly the allylic proton) are more acidic. Unfortunately, the acidity of no other alkene is known as precisely as that of ethylene. 

For acetylenes with adjacent acidic hydrogens the formation of substituted allenes is favored by prototropic rearrangement (Eq. 38). 

Different catalysts bring about different types of isomerization of hydrocarbons. Acids are the best known and most important catalysts bringing about isomerization through a carbocationic process. Brpnsted and Lewis acids, acidic solids, and superacids are used in different applications. Base-catalyzed isomerizations of hydrocarbons are less frequent, with mainly alkenes undergoing such transformations. Acetylenes and allenes are also interconverted in base-catalyzed reactions. Metals with dehydrogenating-hydrogenating activity usually supported on oxides are also used to bring about isomerizations. Zeolites with shape-selective characteristics... 

The selenosulfonates (26) comprise another class of selenenyl pseudohalides. They are stable, crystalline compounds available from the reaction of selenenyl halides with sulftnate salts (Scheme 10) or more conveniently from the oxidation of either sulfonohydrazides (ArS02NHNH2) or sulftnic acids (ArS02H) with benzeneseleninic acid (27) (equations 21 and 22). Selenosulfonates add to alkenes via an electrophilic mechanism catalyzed by boron trifluoride etherate, or via a radical mechanism initiated thermally or photolytically. The two reaction modes produce complementary regioselectivity, but only the electrophilic processes are stereospecific (anti). Similar radical additions to acetylenes and allenes have been reported, with the regio- and stereochemistry as shown in Scheme 11. When these selenosulfonation reactions are used in conjunction with subsequent selenoxide eliminations or [2,3] sigmatropic rearrangements, they provide access to a variety of unsaturated sulfone products. 

Isomerization of acetylenes and allenes.1 HF and BF3 presumably form the acid HBF4 while HF and PF5 form HPF6. Table II shows the approximate times for 20%... 

Formation of allenic acids. Chlorosubstituted acetylenes of the type (1) react with nickel carbonyl to form allenic acids (2). Yields are very low (5-15%),... 

Tarasov, V.V.. Arbisman, Y.S., Kondrat ev, Y.A., and Ivin, S.Z., Investigations in the series of phosphorus-containing compounds with acetylene and allene groupings. Part 3. Infrared spectra of some derivatives of substituted alkynylphosphonic acids, Zh. Obshch. Khim., 38, 130, 1968 J, Gen, Chem. USSR (Engl. Transl.), 38, 129, 1968. 

The sole synthesis of hybridalactone (73) is due to Corey at Harvard. The synthesis involved the use of the novel bicyclo[2.2.2]octyl ortho esters beginning with 62 (Scheme 3.5). This material, obtained from 5-hexynoic acid, was converted via the homologous trimethylsilylmethyl acetylene into allenic iodide 63 in 75% overall yield. 

Propargyl alcohols 339 (R = H, alkyl or Ph R2=H or Me R3 = H, D or alkyl) react with 4-morpholinesulphenyl chloride (340) to yield the rearranged allenic sulphinamides 341, which are converted into the acetylenes 342 by acid-catalysed hydrolysis229. 

Allenic acids, containing the —CH=C=CH— system, occur only rarely in lipids but the known examples are of interest because the glycerides are optically active by virtue of the allene function. Allenic acids are isomeric with acetylenic compounds and each can be rearranged to the other. 

Physiological and Pharmacological Properties Biologically Active Acetylenic Compounds Acetylenes as Phytoalexins Plant-Insect and Plant-Nematode Relationships Phototoxic Effects of Acetylenic Compounds Allenic Fatty Acids References... 

Oxaloacetate decarboxylase, 23 Oxalic acid, 20, 21, 23 Oxamic acid, 20 Oxazolones, 200 6-Oxoestradiol, 89, 479 3-Oxo-5,10-secosteroids, 461-468 synthesis of acetylenic and allenic, 462, 463... 

A full report has been published on the preparation and synthetic applications of the acetylenic dianions (35) of note here is their use in the preparation of allene-l,3-dicarboxylic acids (36). Kolbe co-electrolysis of 5-alkynoic adds, RC=C(CH2)3C02H, with half-esters of diadds Me02C(CH2) C02H followed by saponification gives the coupled product (37) in 45—50% yield. Alternative conditions have been reported for the preparation of oi-acetylenic acids from o>-iodoacids (esp. from fatty acids) using the lithium acetylide-ethylenediamine complex in HMPA. ... 

Gierczak et al. (1997) observed methane, ethylene, acetylene, allene, and propyne as major products formaldehyde, methanol, formic acid, acetic acid, and hydrox-yacetone were identihed as minor products. The mechanism of formation of these products is unclear. Two expected products, observed by Raber and Moortgat (1996), propene and dimethylketene, were not observed, and CO and CO2 products observed by Raber and Moortgat, were not measured by Gierczak et al. (1997). In argon matrix-isolated studies of methacrolein photochemistry (4.2 K) and with A, >300 nm, Johnstone and Sodeau (1992) observed the isomerization of the original trans-methacrolein to di-methacrolein no HCO, CO, or propene could be detected. In similar matrix experiments at A >230 nm, dimethylketene, CO, and propene were observed together with other unidentified products. 

If two equivalents of the reagents are used, disubstitution to ECeC-CH(E)R occurs in most cases, but interestingly the reaction of LiCeCCH(Li)R with an excess of COj gives mainly the allenic dicarboxylic acids. These are probably the result of a rapid isomerization of the primary dilithium salt of the acetylenic diacid during the work-up or during the reaction of the dilithio compound with COj ... 

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