Hydroxyl groups s. Hydroxy

Hydroxylaminolysis 24,38 Hydroxylation s. a. Photo-hydroxylation. Replacement of hydrogen by hydroxyl Hydroxyl groups s. Hydroxy compounds... 

The terminal hydroxyl groups in hydroxy-telechelic polybutadiene are assumed to be predominantly primary alcohols linked to c/s-1,4, trans-1,4, and 1,2 butadiene units [72], Detailed structure of the butadiene or isoprene units at both terminals was studied by the use of 2H-NMR [73], as shown in Section 6.1... 

A general solid-phase approach to ketone-based cysteine protease inhibitors has been reported by Ellman s group [199]. The synthesis of support-bound a-chloro hydrazones key intermediates was achieved by attachment of chlo-romethylketones onto a support-bound hydrazine. The solid-phase synthesis of depsides and depsipeptides has been successfully achieved [200]. The hydroxyl group of hydroxy acids was protected as tetrahydropyranyl ether and couplings to the resin bound chain were performed with DIC/DMAP. 

Another newer version of HALS is exemplified by hydroxy-substituted N-alkoxy hindered amines, i.e., molecules with at least one active moiety of the structure >N-OR-(OH). A very wide range of such additives has been covered in a family of patents assigned to Ciba Speciality Chemicals [193-198], and claims for applications include aromatic polyesters. These additives are said to have as good as or better UV stabilising ability and antioxidant properties as the earlier HALS. The hydroxyl group(s) is said to impart additional advantages not possible with the NOR types, e.g., antistatic attributes, and better pigment dispersion in polar polymers. 

Hydroxyl groups (s. a. Hydroxy compounds, Steroid hydroxyl groups)... 

Quinones Barrier [6] has separated some benzoquinones on silica-starch layers, using hexane-ethyl acetate (85 + 15). Pettersson [169] later made a detailed comparison of the chromatographic behaviour of benzoquinones, of which 31 contained hydroxyl group(s) and 21 were without. Neutral solvents, especially mixtures of benzene-chloroform and xylene, were suitable for the last named. The basic solvent VIII (Table 166) was better for the more polar hydroxy-quinones they migrate as enolates in this system. The hi /-values on silica gel layers of some recently discovered [170] fungus colouring materials are given below they were obtained with solvent VIII (values without brackets) and chloroform (values in brackets) ... 

The low amounts of A -THC and 7-hydroxy-A -THC excreted in the urine seem to be a result of further metabolism yielding more polar compounds with the 7-methyl group being further oxidized to a carboxyl group via the aldehyde (4) with or without introduction of additional hydroxyl group(s). The A -THC-7-oic acid has been identified as a major metabolite in urine, faeces, and plasma from humans given A -THC or 7-hydroxy-A -THC i.v. (3). 

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

Pyrazoles, isoxazoles and isothiazoles with a hydroxyl group in the 3-position (491 Z = NR, O, S) could isomerize to 3-azolinones (492). However, these compounds behave as true hydroxy derivatives and show phenolic properties. They give an intense violet color with iron(III) chloride and form a salt (493) with sodium hydroxide which can be O-alkylated by alkyl halides (to give 494 R = alkyl) and acylated by acid chlorides (to give 494 R = acyl). 

Because the pK s of the aldehyde and water are similar, the solution contains significant quantities of both the aldehyde and its enolate. Moreover, their reactivities are complementary. The aldehyde is capable of undergoing nucleophilic addition to its carbonyl group, and the enolate is a nucleophile capable of adding to a carbonyl group. And as shown in Figure 18.4, this is exactly what happens. The product of this step is an alkoxide, which abstracts a proton from the solvent (usually water or ethanol) to yield a (3-hydroxy aldehyde. A compound of this type is known as an aldol because it contains both an aldehyde function and a hydroxyl group (aid + ol = aldol). The reaction is called aldol addition. 

Ionization constants of czs-3-substituted acrylic acids have been correlated with the Hammett equation by Hogeveen (58) and by Charton (60). Charton has correlated ionization constants for a number of other c/s-vinylene sets with the Hammett equation (60). Charton and Charton have correlated some cw-vinylene sets with the extended Hammett equation [eq. (2)] (73). Sufficient data are available for twelve sets of cis-vinylene equilibria, of which four sets represent ionization constants of hydroxy compounds (sets 12-1 to 12-4) and eight sets represent ionization constants of carboxylic acids (sets 12-5 to 12-12). All sets have been correlated with eq. (24) and eq. (2). Sets studied are reported in Table XII. Results of the correlations are reported in Table XIII. Sets designated A were correlated with eq. (24), sets designated B were correlated with eq. (2). In the case of the second ionization constant of 2,3,5,6-tetrahydroxy-l,4-benzoquinone (set 12-3), it is uncertain which hydroxyl group ionizes therefore, the value for X = OH was excluded from the correlation. All of the sets 12-1 to 12-4 gave significant correlations with both eq. (24) and eq. (2),... 

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