Alkyl fission

Transesterification occurs by mechanisms that are identical with those of ester hydrolysis—except that ROH replaces HOH—that is, by the acyl-oxygen fission mechanisms. When alkyl fission takes place, the products are the acid and the ether. 

Dinitrophenyl (DNP) derivatives are useful for the separation and the subsequent MS identification of amines [207]. Most of the derivatives give reasonably intense molecular ions and an ion at m/e 196, which is usually the base peak formed by a-alkyl fission. A similar TLC separation and MS identification is also possible by converting aliphatic amines into 4-nitroazobenzene4-carboxylic acid amides [208]. The molecular ions are relatively intense (the second most abundant ion) and the base peak corresponds in all cases to a fragment at m/e 254. 

The mechanism and kinetics of the sulfation of the lower alcohols with sulfuric acid have been studied. The reaction proceeds by a bimolecular displacement mechanism like that of the acid-catalyzed esterification of alcohols with carboxylic acids no oxygen-alkyl fission occurs. Neopentyl alcohol sulfates at a rate comparable to other secondary alcohols these results indicate that within the groups of primary and secondary alcohols steric effects are minor. However, primary alcohols sulfate at a rate ten times that of secondary alcohols. The experimentally determined rate law... 

Polystyrene (soluble), incorporating an arylsul-phonyl chloride group Polymer-saccharide (C-6) sulphonate ester" O-Alkyl fission of sulphonate ester AcOK-DMF /3-D-Gentiobiose octaace-tate Guthrie e/a/., 1971, 1973... 

Alkaline saponification of polymer-bound sugar ester did not proceed very smoothly, but when polymer-sulfonate sugar esters were employed, the cleavage involving detosylation and O-alkyl fission of the sulfonate ester (KOAc-DMF) proceeded smoothly (Guthrie et at., 1973), producing 0-acetates. From this it may be concluded that the OAc group is not affected under these conditions. 

A most peculiar and, a priori, unlikely process has been reported, where the strong base-weak nucleophile l,5-diazabicyclo[4,3,0]non-5-ene cleaves hindered methyl esters by O-alkyl fission the authors exclude the possibility of simple hydrolysis, as no reaction is observed with unhindered esters. 

General.—new type of basic amide hydrolysis, characterized by N-alkyl fission, has been reported, and is exemplified in Scheme 53. 

Acyl fission merely regenerates starting materials. The acid-catalyzed hydrolysis of tcrt-butyl acetate proceeds by an SnI process (stable carbonium intermediate) with alkyl fission. 

The anionic product causes electrostatic repulsion of any incoming hydroxide, so that monomethyl phosphate will not readily form. The half-life of this latter reaction is 16 days at 100°C, and the mechanism involves exclusively alkyl fission as the phosphorus atom is less accessible ... 

The reaction is carried out in aqueous dioxane. Remember, the aldoximes are good nucleophiles, as dictated by the a-effect. Recently, the methyl group has found use as its removal by alkyl fission with good nucleophiles (thio-phenoxide, butylamine) also reduces intemucleotide cleavage (365). 

The susceptibihty of dialkyl peroxides to acids and bases depends on peroxide stmcture and the type and strength of the acid or base. In dilute aqueous sulfuric acid (<50%) di-Z fZ-butyl peroxide is resistant to reaction whereas in concentrated sulfuric acid this peroxide gradually forms polyisobutylene. In 50 wt % methanolic sulfuric acid, Z fZ-butyl methyl ether is produced in high yield (66). In acidic environments, unsymmetrical acychc alkyl aralkyl peroxides undergo carbon—oxygen fission, forming acychc alkyl hydroperoxides and aralkyl carbonium ions. The latter react with nucleophiles,... 

Isoquinoline also forms Reissert compounds when treated with benzoyl chloride and alkyl cyanide (28), especially under phase-transfer conditions (29). The W-phenylsulfonyl Reissert has been converted to 1-cyanoisoquinoline with sodium borohydride under mild conditions (154). When the AJ-benzoyl-l-alkyl derivative is used, reductive fission occurs and the 1-alkyLisoquinoline is obtained. 

Unsubstituted 3-alkyl- or 3-aryl-isoxazoles undergo ring cleavage reactions under more vigorous conditions. In these substrates the deprotonation of the H-5 proton is concurrent with fission of the N—O and C(3)—-C(4) bonds, giving a nitrile and an ethynolate anion. The latter is usually hydrolyzed on work-up to a carboxylic acid, but can be trapped at low temperature. As shown by Scheme 33, such reactions could provide useful syntheses of ketenes and /3-lactones (79LA219). 

Thiazolidine-2,4-dione, 2-dialkylamino-bisimide synthesis, 5, 129 Thiazolidine-2,4-diones IR spectroscopy, 6, 242 tautomerism, 6, 270 Thiazolidine-2,5-diones synthesis, 5, 138 Thiazolidine-4,5-diones synthesis, 5, 129 6, 316-317 Thiazolidine-2,4-dithiones tautomerism, 6, 270 Thiazolidines "C NMR, 6, 243 conformation, 6, 242, 247 dihydrothiazines from, 2, 93 hydrolysis, 6, 273 IR spectra, 6, 242 ring fission, 5, 80 synthesis, 5, 118 6, 316-321 Thiazolidines, imino-tautomerism, 6, 273 Thiazolidines, methyl-conformation, 6, 242 Thiazolidine-2-thione, 3-acyl-reduction, 1, 469 Thiazolidine-2-thione, 4-alkyl-synthesis, 6, 318... 

The results shown for compounds (26)-(29) and (36) suggest that a rather subtle balance of various factors has to be considered for a prediction of relative yields and structures of products. Although fission of the more highly alkyl substituted bond by a-cleavage proceeds with a high degree of selectivity in the primary photochemical step, the subsequent disproportiona-... 

The designation Ac signifies acyl-oxygen fission, whereas A1 is alkyl-oxygen fission. When n-amyl alcohol was hydrolyzed in 0-enriched water, the 0 appeared in the product acid rather than the alcohol, showing that alkyl-oxygen fission could not have occurred. Carpenter gives many examples of isotopic studies. 

Al, as shown in structure 3), the molecularity (1 or 2), and the ionic form of the substrate [A for conjugate acid RC(OH)OR and B for conjugate base RCOOR]. Note that alkyl-oxygen fission constitutes nucleophilic substitution and is therefore equivalent to the classification ... 

There has as yet been no systematic work on the mass spectra of cyclic hydroxamic acids, but from the limited information available the direct loss of 0 or OH from the molecular ion is to be expected. The fragmentation behavior of the 0-alkyl derivatives is rather unpredictable, although again processes involving fission of the N—0 bond are generally important. Table II shows the prominent first-generation fragment ions from a few hydroxamic acids and their ethers. 

Oxaziranes derived from isobutyraldehyde react with ferrous salts to give only substituted formamides fEq. (23)], The chain propagating radical 30 thus suffers fission with elimination of the isopropyl group. An H-transfer would lead to substituted butyramides, which are not found. Here is seen a parallel to the fragmentation of alkoxyl radicals, where the elimination of an alkyl group is also favored over hydrogen. The formulation of the oxazirane fission by a radical mechanism is thus supported. 

For the reaction in the gas phase, Emmons proposes a liomolytic O—N fission and (possibly simultaneous) alkyl shift [Eq. (28)]. The... 

With aldehydes some diaziridines condense under the conditions of preparation. The formation of a fused triazolidine ring occurs regularly if aldehydes are treated with ammonia and chloramine to give diaziri-dines [Eq. (39)]. If, however, chloral is added previously to the reaction mixture, the 3-aIkyl-diaziridines (45) arc caught as their chloral adducts. By the alkali fission of these chloral adducts, 3-alkyl-diaziridines, e.g. (45), can be prepared. 

Sulfones are thermally very stable compounds, diaryl derivatives being more stable than alkyl aryl sulfones which, in turn, are more stable than dialkyl sulfones allyl and benzyl substituents facilitate the homolysis by lowering the C—S bond dissociation energy17. Arylazo aryl sulfones, on heating in neutral or weakly basic media at 100°C, yield an aryl and arenesulfonyl radical pair via a reversible one-bond fission followed by dediazoni-ation of the aryldiazenyl radical (see Scheme 2 below)20. However, photolysis provides a relatively easy method for generating sulfonyl radicals from compounds containing the S02 moiety. 

A possible alternative mechanism for the formation of fragment alkyl ions comes immediately to mind—namely, beta fission of the Ci8 ion formed in Reactions 6 and 7 to form a smaller alkyl ion and an olefin. Thus we write as a typical example ... 

Thus we think of the chemical ionization of paraffins as involving a randomly located electrophilic attack of the reactant ion on the paraffin molecule, which is then followed by an essentially localized reaction. The reactions can involve either the C-H electrons or the C-C electrons. In the former case an H- ion is abstracted (Reactions 6 and 7, for example), and in the latter a kind of alkyl ion displacement (Reactions 8 and 9) occurs. However, the H abstraction reaction produces an ion oi m/e = MW — 1 regardless of the carbon atom from which the abstraction occurs, but the alkyl ion displacement reaction will give fragment alkyl ions of different m /e values. Thus the much larger intensity of the MW — 1 alkyl ion is explained. From the relative intensities of the MW — 1 ion (about 32%) and the sum of the intensities of the smaller fragment ions (about 68%), we must conclude that the attacking ion effects C-C bond fission about twice as often as C-H fission. 

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