Methoxylations

Pectin also contains araban and galactan. Il is present in fruits, root vegetables and other plant products, and confers on jams their typical gelling property. Pectin is manufactured as a white powder, soluble in water, and used to assist the setting of jams and jellies, and for numerous other purposes. Low melhoxyl pectins, with under 7% methoxyl, give firmer gels than pectins proper. 

In the cases of 4-hydroxyquinoline and 4-methoxyquinoline the predominance of 6-nitration supports the evidence presented above that nitration in sulphuric acid proceeds via the cations. For both these compounds reaction via the neutral molecules would be expected to occur to a considerable extent at C(j) as a result of the directing properties of the hydroxyl and methoxyl groups. 

Figure 7.6 Chemical shift (from hexamethyldisiloxane) for acrylonitrile-methyl methacrylate copolymers of the indicated methyl methacylate (Mj) content. Methoxyl resonances are labeled as to the triad source. [From R. Chujo, H. Ubara, and A. Nishioka, Polym. J. 3 670 (1972).]...

Pectin. Pectin [9000-69-5] is a generic term for a group of polysaccharides, mainly partially methoxylated polygalacturonic acids, which are located in the cell walls of all plant tissues. The main commercial sources of pectin are citms peel and apple pomace, where it represents 20—40% and 10—20% of the dry weight respectively. The pectin is extracted, the extract purified, and the pectin precipitated (50) increased extraction times lead to the production of low methoxyl pectins. 

Pectins are generally classed according to their ester content as high methoxyl pectins (>50% of the carboxyl groups esterified) or low methoxyl pectins (<50% of carboxyl groups esterified) (pectic acid, methyl ester [9049-34-1]). Low methoxyl pectins, like algins, require calcium for gelation. 

A simple synthesis of tetrahydroxyben2oquinone by methoxylation—hydrolysis of chloranil has been reported (265). Similarly, tetraar5ioxyben2oquinones have been prepared from chloranil and alkali salts of phenols (266). 

Although the activity of methoxylated monobactams could be improved by appropriate side-chain modifications, difficulty of synthesis and poor chemical stabihty focused attention on the nonmethoxylated analogues. Both high intrinsic activity and excellent P-lactamase stabiUty are exhibited by monobactams that combine C-3 arninothia2ole oxime side chains and 4-alkyl, 4-alkenyl, and 4-alkynyl groups (19). 

Pectins are subdivided according to their degree of esterification (DE), a designation of the percent of carboxyl groups esterified with methanol. Pectins with DE >50% are high methoxyl pectins (HM pectins) [65546-99-8]-, those with DE <50% are low methoxyl pectins (LM pectins) [9049-34-7]. 

Flavone dyes having these stmctures are hydroxylated and methoxylated derivatives. The degree of hydroxylation varies from two in chrysin [480-40-0] (17) to six in gossypetin [489-35-0] (18). Those dyes containing not more than three hydroxyls are generally termed flavones whereas those containing up to and including six are flavonols. 

The conversion of furans by oxidative acetylation or methoxylation to 2,5-diacetoxy- or 2,5-dimethoxy-2,5-dihydrofurans respectively, and their subsequent hydrogenation to the corresponding tetrahydrofurans, provides a useful source of protected 1,4-dicarbonyl compounds capable of conversion inter alia into the other five-membered heterocycles [Pg.142]

Generation of an anion at the 3-position of certain 2-methoxyisoxazolidines leads to loss of the A-methoxyl group (Scheme 92) (79T213). 

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