Hydroxyl groups, free

Analysis There is a series of 1,2 relationships here ifs easiest to start with the free hydroxyl group ... 

This reaction has been used m an imaginative way to determine the ring size of glycosides Once all the free hydroxyl groups of a glycoside have been methylated the glycoside is subjected to acid catalyzed hydrolysis Only the anomeric methoxy group IS hydrolyzed under these conditions—another example of the ease of carbocation for matron at the anomeric position... 

Reducing sugar (Section 25 19) A carbohydrate that can be oxidized with substances such as Benedict s reagent In general a carbohydrate with a free hydroxyl group at the anomenc position... 

Acetic anhydride acetylates free hydroxyl groups without a catalyst, but esterification is smoother and more complete ia the presence of acids. For example, ia the presence of -toluenesulfonic acid [104-15-4], the heat of reaction for ethanol and acetic anhydride is —60.17 kJ/mol (—14.38 kcal/mol) (13) ... 

Partial glycerides tend to melt higher than thek triglyceride counterparts, as shown in Figure 6. This observation is consistent with the presence of free hydroxyl groups which can participate in increased intermolecular hydrogen bonding. 

As Eigure 1 implies, there is usually some residual acidity as well as free hydroxyl groups left in the resin molecules. Stmcture-property relationships and the principles commonly followed to design the resin stmcture are discussed later. 

Every polysaccharide contains glycosyl units with unsubstituted hydroxyl groups available for esterification or etherification. Polysaccharide derivatives are described by their degree of substitution (DS), which is the average number of substituent groups per glycosyl unit. Because each monomeric unit of cellulose molecules has free hydroxyl groups at C-2, C-3, and C-6, the maximum DS for cellulose, and all polysaccharides composed exclusively of neutral hexosyl units, the majority of polysaccharides, is 3.0. 

Substrates. The principal use for reactive dyes is dyeing textiles ceUulosics constitute the largest use. Cotton is very nearly pure cellulose, and as such has three free hydroxyl groups per glucoside unit that act as dye sites for reactive dyes. 

Monoprotection of a symmetrical diol can be effected by reaction with a polymer-supported phenylacetyl chloride. The free hydroxyl group is then converted to an ether and the phenylacetate cleaved by aqueous ammonia-dioxane, 48 h. ... 

It is suggested that in valeriodine the free hydroxyl group is at C or C , as in the above partial formula, and the esterified hydroxyl group at C , as is usual in this series (cf. hyoscyamine, p. 79). 

Anhalamine. When mezcaline is condensed with formaldehyde it yields 6 7 8-trimethoxy-l 2 3 4-tetrahydrowoquinoline and the quaternary iodide obtained from this is identieal with dimethylanhalamine methiodide. It follows that 0-methylanhalamine must be 6 7 8-trimethoxy-1 2 3 4-tetrahydrot5oquinoline. The free hydroxyl group was shown to be at C by Spath and Beeke, who found that the produet (II R = Et), formed by 0-ethylation of anhalamine, gave 4 5-... 

The position of the free hydroxyl group in these two alkaloids is either C or C , since Spath has shown that the OiV-diacetyl derivative of -5-hydroxy-3 4-dimethoxyphenylethylamine, when heated in toluene solution with phosphoric oxide, yields a product which must be either 6-acetoxy-7 8-dimethoxy-, or 8-acetoxy-6 7-dimethoxy-l-methyl-3 4-dihydrowoquinoline. On reduction with tin and hydrochloric acid t is converted into anhalonidine, which must therefore be 6-hydroxy-7 8-dimethoxy- (or 8-hydroxy-6 7-dimethoxy-)-l-methyl-l 2 3 4-tetrahydrofsoquinoline. Similarly the methiodide of the acetoxy-com-pound on reduction yields, by loss of acetic acid and addition of two hydrogen atoms, pellotine, proving the latter to be A -methylanhalonidine. The position of the free hydroxyl group was finally shown by Spath to... 

In a similar attempt, Decker and Eichler reduced A -methylnor-papaverinium phenolbetaine (VIII) with tin and hydrochloric acid and obtained i/i-laudanine, m.p. 112°, pierate, m.p. 162-3°, which was subsequently investigated by Spath and Epstein, who showed that on methylation it furnished dMaudanosine and that the ethyl ether on energetic oxidation yielded veratric acid (3 4-dimethoxybenzoic acid) and the methyl ethyl ether of nor-m-hemipinic acid. This clearly indicated that the free hydroxyl group was in the woquinoline nucleus, and its position was determined by the fact that on mild oxidation 7-methoxy-6-ethoxy-l-keto-2-methyl-l 2 3 4-tetrahydrowoquinoline, m.p. 95-6°, was produced, and on this basis these authors assigned formula (IX R = H R = CH3) to -laudanine. 

Constitution. Comparison of the empirical formula of the three alkaloids, and the fact that jatrorrhizine and columbamine each stands to palmatine in the relation of a monohydric phenol to its methyl ether, makes it clear that the only difference between jatrorrhizine and columbamine must be in the position of the free hydroxyl group. The method by which this point was settled is described in dealing with the two tetrahydro-derivatives of these alkaloids (p. 291). The constitution of palmatine (XXV R = R = Me) is dealt with under tetrahydropalmatine, but it is still necessary to describe the complete synthesis of this alkaloid via oxypalmatine (XXVII) and tetrahydropalmatine. 

Esters and acetylated hydroxyl groups are completely stable under the experimental conditions, but with ketals 10 29,110,112 yields are generally observed in the thermal reaction. Double bonds do not seem to interfere seriously with the course of the reaction provided that the geometric relationship of the free hydroxyl group to the angular methyl group is not changed drastically. In some cases allylic acetoxylation occurs, e.g., at C-7 of A -steroids. ° Ketones are usually stable (especially under photo-lytic conditions) but occasionally a-acetoxylation has been observed. 

Olid carbon is asymmetric. The various acylglycerols are normally soluble in benzene, chloroform, ether, and hot ethanol. Although triacylglycerols are insoluble in water, mono- and diacylglycerols readily form organized structures in water (discussed later), owing to the polarity of their free hydroxyl groups. 

The importance of the o-hydroxyl moiety of the 4-benzyl-shielding group of R,R-BOX/o-HOBn-Cu(OTf)2 complex was indicated when enantioselectivities were compared between the following two reactions. Thus, the enantioselectivity observed in the reaction of O-benzylhydroxylamine with l-crotonoyl-3-phenyl-2-imi-dazolidinone catalyzed by this catalyst was 85% ee, while that observed in a similar reaction catalyzed by J ,J -BOX/Bn.Cu(OTf)2 having no hydroxyl moiety was much lower (71% ee). In these reactions, the same mode of chirality was induced (Scheme 7.46). We believe the free hydroxyl groups can weakly coordinate to the copper(II) ion to hinder the free rotation of the benzyl-shielding substituent across the C(4)-CH2 bond. This conformational lock would either make the coordination of acceptor molecules to the metallic center of catalyst easy or increase the efficiency of chiral shielding of the coordinated acceptor molecules. 

Under basic conditions, the cleavage would be initiated by deprotonation of a free hydroxyl group, as shown in 4. 

Polyurethanes are essentially the reaction products of polyisocyanates and polyesters containing free hydroxyl groups. They are comparable with the... 

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