Vicinal Glycols

For many purposes, such as formation of cyclic derivatives of glycols, vicinal cis groups attached to the cyclopentane ring may be considered to... 

Periodic Acid Test for vic-Glycols. Vicinal glycols (hydroxyl groups on adjacent carbon atoms) can be detected by reaction with periodic acid. In addition to 1,2-glycols, a positive test is given by a-hydroxy aldehydes, a-hydroxy ketones, a-hydroxy acids, and a-amino alcohols, as well as 1,2-diketones. 

Lead(fV) ethanoate, Pb(02CCH3)4, (Pb(ll)ethanoate plus CI2) is a powerful oxidizing agent which will convert vicinal glycols to aldehydes or ketones and 1,2-dicarboxylic acids into alkenes. Primary amides give ketones and amines give nitriles. 

The reaction is based, on the one hand, on the oxidative cleavage of vicinal diols by lead(IV) acetate and, on the other hand, on the reaction of dichlorofluorescein with lead(IV) acetate to yield a nonfluorescent oxidation product. The dichlorofluorescein only maintains its fluorescence in the chromatogram zones where the lead(IV) acetate has been consumed by the glycol cleavage reaction [1],... 

A classical method for the vicinal hydroxylation of a double bond involves treatment with osmium tetroxide to give a cyclic ester, followed by reductive cleavage to the glycol ... 

Vicinal glycols may be oxidized to the corresponding 17a-hydroxy-20-ketones in reasonable yields by means of chromium trioxide in dimethylfor-mamide in the presence of manganese dichloride, or by treatment with dimethyl sulfoxide-acetic anhydride. ... 

Base catalyzed pinacol rearrangement of vicinal m-glycol monotosylates is a simple and useful general method for preparing perhydroazulenes. Thus, treatment of cholestane-5a,6a-diol 6-tosylate (115a) with either one mole-equivalent of potassium t-butoxide in f-butanol at 25° or with calcium carbonate in dimethylformamide at 100° gives a quantitative yield of 10(5 6/5H)... 

In theory, periodate oxidation could have given a clear-cut answer as to the composition of the isomeric mixture of deoxy ribose phosphates. The 4-phosphate (73), devoid of vicinal diol groups, should be resistant to periodate the 3-phosphate (74) should reduce one and only one molar equivalent of the oxidant and yield one molar equivalent of both formaldehyde and the phosphorylated dialdehyde (75), whereas the 5-phosphate (76) could be expected to reduce one molar equivalent of periodate relatively rapidly, followed by a slower overoxidation reaction owing to the oxidation of malonaldehyde, formed as a result of the glycol cleavage. 

Epoxides are cleaved by treatment with acid just as other ethers are, but under much milder conditions because of ring strain. As we saw in Section 7.8, dilute aqueous acid at room temperature is sufficient to cause the hydrolysis of epoxides to 1,2-diols, also called vicinal glycols. (The word vicinal means "adjacent/ and a glycol is a diol.) The epoxide cleavage takes place by SK2-like backside attack of a nucleophile on the protonated epoxide, giving a trans- 1,2-dio) as product. 

Vicinal hydroxyl groups, as in an ethylene glycol unit, have conformational attributes that can be described by using acyclic orientational notation... 

In the pyranoses in the chair conformations, the vicinal hydroxyl groups can exist only in the anticlinal or gauche orientations. The gauche arrangement of a-glycols is normally encountered as diequatorial or axial-... 

It is an important reagent for the oxidative cleavage of vicinal glycols which are oxidised at room temperatures to aldehydes, ketones or both depending on the nature of glycol. 

Since the cleavage of vicinal glycols is acid or base catalysed, the following ionic mechanism ... 

Like lead tetra acetate, periodic and also cleaves vicinal glycols very smoothly and forms carbonyl compounds. The reaction introduced by Malaprade in 1928 may be represented as ... 

The mechanism of oxidation of vicinal glycols by HI04 has been studied by G.J. Buisst and C.A. Bunton (J. Chem. Soc., 1406, (1954). According to these workers, the reactive species is the para form of periodic acid (H5I06) which is formed by the action of water on HI04. 

In five-membered rings large negative deviations from additivity have been observed as well (315,322,323). In eclipsed c/j-glycols the ICS values can be as large as - 15 (315,322) they are somewhat smaller if vicinal bromo, azido, or acetamido substituents are involved. As a rule, upfield ICSs are palpably reduced in the trans isomers (322,323), especially for carbon atoms bearing less electronegative substituents, such as Br, SH, and N3. 

In the example above, a short-chain poly(ethylene glycol) was added to a rigid polyelectrolyte to plasticise the material and thereby increase polymer-solvent motion in the vicinity of mobile ions. This strategy has been widely explored as a means of improving ion transport in electrolytes. 

Mechanisms involving glycol bond fission have been proposed for the oxidation of vicinal diols, and hydride transfer for other diols in the oxidation of diols by bromine in acid solution.The kinetics of oxidation of some five-ring heterocyclic aldehydes by acidic bromate have been studied. The reaction of phenothiazin-5-ium 3-amino-7-dimethylamino-2-methyl chloride (toluidine blue) with acidic bromate has been studied. Kinetic studies revealed an initial induction period before the rapid consumption of substrate and this is accounted for by a mechanism in which bromide ion is converted into the active bromate and hyperbromous acid during induction and the substrate is converted into the demethylated sulfoxide. 

A term used to designate the geometric arrangement of moieties attached to two adjacent atoms within a molecule. An example of a vicinal diol would be ethylene glycol (HOCH2CH2OH) and a vicinal dihalide would be 1 -bromo-2-chloroethane. 

Incorporation of glycol or vicinal diol analogs of the peptide bond (-CH(OH)-CH(OH)-) has led to potent inhibitors and the x-ray structure for one such compound complexed with endothiapepsin is available [27]. The first hydroxyl in... 

Synthesis of the cyclic acetal 25 in 63% yield by reaction of the unsaturated bromo-nitrilo sugar 24 (E configuration) with ethylene glycol in the presence of sodium hydroxide has been reported.40 An extension of this work was given for sugars having a vicinal diol... 

The observed rate constants kobs have been measured over a pH range of 1-12 by the stopped-flow method. The general expression for kobs corresponding to the reaction system described by Eqs. (31) and (32) is closely related to Eq. (3U).222 The relative weights of the reverse and forward reaction terms are, however, appreciably different under varying conditions. Unlike the reaction of 160 in water, where the attack of H20 prevails in the vicinity of pH 6, under no conditions is the reaction of the unionized glycol ether (plateau portion of the forward reaction plot) important. 

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