Methanol self-condensation

Thus the reactions of cyclic or acyclic enamines with acrylic esters or acrylonitrile can be directed to the exclusive formation of monoalkylated ketones (3,294-301). The corresponding enolate anion alkylations lead preferentially to di- or higher-alkylation products. However, by proper choice of reaction conditions, enamines can also be used for the preferential formation of higher alkylation products, if these are desired. Such reactions are valuable in the a substitution of aldehydes, which undergo self-condensation in base-catalyzed reactions (117,118). Monoalkylation products are favored in nonhydroxylic solvents such as benzene or dioxane, whereas dialkylation products can be obtained in hydroxylic solvents such as methanol. The difference in products can be ascribed to the differing fates of an initially formed zwitterionic intermediate. Collapse to a cyclobutane takes place in a nonprotonic solvent, whereas protonation on the newly introduced substitutent and deprotonation of the imonium salt, in alcohol, leads to a new enamine available for further substitution. 

Chlorophthalazine is quite reactive to many basic nucleophiles but reacts sluggishly with aqueous or alcoholic alkali. In contrast, it is very rapidly hydrolyzed by warm, concentrated hydrochloric acid as are its diazine isomers. In hydrolysis with very dilute acid or with water, it forms some phthalazinone but mostly the self-con-densation product which hydrolyses to give 2-(l -phthalazinyl)-phthalazin-l-one (70% yield). Such self-condensations in diazanaph-thalenes and in monocyclic azines are always acid-catalyzed (Sections II, C and III,B). With methanolic methoxide, 1-chlorophthalazine (65°, few mins), its 7-methoxy analog (20°), and 1,6- and 1,7-dichlorophthalazines (20°) readily undergo mono-substitution. 

Symmetrically substituted dipyrrylmethanes, for example (130), are less generally useful in porphyrin syntheses, but they can be prepared efficiently by self condensation of 2-acetoxymethylpyrroles, e.g. (131) in HCl/methanol, or by heating 2-bromomethylpyrroles, e.g. (132) in methanol. 

A further frequent complication is that acetylenic esters undergo base and acid-catalyzed self-condensation on standing under normal laboratory conditions, and they will add methanol or similar nucleophiles in Michael-type addition reactions (cf. 4 and 6). Such products are almost invariably present in reaction mixtures obtained from heterocycles. A short account of these products is included as their early recognition in a new investigation can save much time. 

Grubb considered this problem in detail and concluded (24) that under these conditions the reaction of silanols with methanol is rapid compared to self-condensation. Even under milder conditions the self-condensation of silanols is not complete when much alcohol is present, but an equilibrium is established in which most of the silanol is present as alkoxysilane. Grubb discussed the equilibria involved ... 

Catalytic hydrogenation of 2-nitromethylenehexahydro-l//-azepine (1, R = H) over palladized charcoal in acidic methanol afforded 2,5-bis(5-aminopentyl)pyrazine (2, R = H) (67%, as hydrochloride)by reduction of the nitro group, 1,2-fission, and self-condensation of the unsaturated product 145, 467 the 1-methylated substrate (1, R = Me) likewise gave 2,5-bis(5-methylaminopentyl)pyrazine (2, R = Me) but only in 10% yield.145... 

Addition of the anion of 2-methyl-l,3-cyclopentadione (348) to protoane-monin (349), easily prepared from levulinic acid in four steps (207), led to adduct 350 in low yield due to ready self-condensation (Scheme 39). Transesterification with acidic methanol set the alcohol free, which cyclized spontaneously to the 1 1 mixture of ketals 351 and 352. To enhance the yield of the ketal 352, ketal 351 was recycled by equilibration in acidic methanol. Under Kharash-Grignard conditions, the isopropenyl group added unselectively in 1,4-mode and the ester enolate 353... 

The RTV silicones contain methoxy groups substituted along the polysiloxane chain, which react with moisture to form silanol groups, which undergo self-condensation to form cross-links. Methanol is produced as a byproduct. 

A synthesis of dicyclopropyl ketone developed by Hart and co-workers involves in the first step a sodium methoxide-catalyzed self-condensation of y-butyrolactone (1) to the dimeric product (2). Solvent methanol is removed by distillation, eventually... 

Carbenes were the earliest proposed Cl intermediates. These were considered to be generated via a-elimination of water from methanol itself [9,10], or from catalyst surface methoxyls [11]. The reaction may be assisted by cooperative action of acid and base sites on the catalyst [10]. Olefins would be formed by polymerization of the (free) CIl2. To overcome the high energetic requirements of carbene generation (vide infra), and the low probability of CH2 self-condensation, Chang and Silvestri [lb] proposed a concerted mechanism of carbene generation with sp3 insertion into the C-H bond of DME to form MeOEt. 

In the above condensation resist designs, the phenolic resin offers a reaction site as well as base solubility. Self-condensation of polymeric furan derivatives has been utilized as an alternative crosslinking mechanism for aqueous base development (Fig. 126) [375]. The copolymer resist is based on poly[4-hydroxy-styrene-co-4-(3-furyl-3-hydroxypropyl)styrene], which was prepared by radical copolymerization of the acetyl-protected furan monomer with BOCST followed by base hydrolysis. The furan methanol residue, highly reactive toward electrophiles due to a mesomeric electron release from oxygen that facilitates the attack on the ring carbons, readily yields a stable carbocation upon acid treatment. Thus, the pendant furfuryl groups serve as both the latent electrophile and the nucleophile. Model reactions indicated that the furfuryl carbocation reacts more preferentially with the furan nucleus than the phenolic functionality. 

Fig. 126 Acid-catalyzed self-condensation of polymeric furan methanol...

Monomeric partially and fully alkylated amino resins are prepared in two separate reaction steps. Hydroxymethylation is carried out under basic conditions to minimize self-condensation of the amino resin. The pH is then lowered by addition of a mineral acid and alkylation with methanol is carried out. To obtain monomeric amino resins, an excess of formaldehyde has to be used to assure a high level of hydroxymethylation and a low level of residual amide groups that would otherwise lead to polymer formation during the alkylation step. Since water removal by azeotropic distillation is not possible with methanol, a large excess of alcohol is required to achieve complete alkylation. After completion of alkylation the resin solution is neutralized water, alcohol, and residual formaldehyde are removed by vacuum distillation. The salt formed during neutralization is removed by filtration [2.154]. 

The self-condensation of sulfonoimidoyl chlorides such as A/ -tosyl (Ts) derivative of the benzene- and 4-phenoxybenzene-sulfonimidoyl chloride (142) utilizing a catalytic (AICI3 or FeCla) Friedel-Crafts reaction has been studied as a way to produce these polymers. It has been foimd that the reaction of the former compound yielded no polymeric product, whereas that of (142) produced exclusively methanol-insoluble polymer (143) of Mn = 14,500 with polydispersity = 1.45 in 80% yield (317). 

The most commonly used alcohols are methanol, butanol, isobutanol and 2-ethylhexanol. Self-condensation of the methylolmelamines also occurs during etherification so that melamine resins typieally contain an appreciable quantity of dimers, timers and higher oligomers. 

I Self-Test 19.1 A (a) Write the condensed structural formula of the ester formed from the reaction between propanoic acid, CH3CFI2COOH, and methanol, CH3OH. 

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