Hexane-1,6-diol oxidation

Tri-n-hexylborane reacts at ca. 200°C with 2 equiv HjB-NEtj to give mixed B-hexylboracyclanes. Their oxidation with alkaline H2O2 produces 1,4- and 1,5-hexane-diols and 1-hexanol as the major products. Small amounts of 1,6-hexanediol and 2-hexanol are also obtained . 

Potassium salts of the monosubstituted Keggin POMs, [PWjjMO q] , (M=Co(II), Ni (II), Cu(II), Zn(II)), were used as catalysts for lactonization of 1,4-butane diol, 1,6-hexane diol, and 1,2-benzene dimethanol in the presence of hydrogen peroxide as an oxidant. The effects of various parameters such as amount of the oxidant and diol, solvent type, temperature, and reaction time have been studied. The results show that [PWjjCoO ] as a catalyst in chloroform produce the highest yield of lactone [105] (Scheme 3.45). 

The oxacycles have remained a more challenging synthetic task as compared to the N- and S-containing medium sized rings. The medium sized lactones have also attracted significant attention as these are considered to be a rare class of organic compounds, which are even difficult to produce in natural biosynthetic pathways (Shiina, 2007). Bagley et al. (2009) reported microwave-assisted synthesis of seven membered lactones through a tandem oxidation- cyclocondensation of 1,6-hexane-diol. 

Cyclohexadiene has been prepared by dehydration of cyclohexen-3-ol,3 by pyrolysis at 540° of the diacetate of cyclohexane-1,2-diol,4 by dehydrobromination with quinoline of 3-hromocyclohexene,6 by treating the ethyl ether of cyclohexen-3-ol with potassium bisulfatc,6 7 by heating cyclohexene oxide with phthalic anhydride,8 by treating cyclohexane-1,2-diol with concentrated sulfuric acid,9 by treatment of 1,2-dibromocyclo-hexane with tributylamine,10 with sodium hydroxide in ethylene glycol,10 and with quinoline,6 and by treatment of 3,6-dibromo-cyclohexene with sodium.6... 

The production of alcohols by the catalytic hydrogenation of carboxylic acids in gas-liquid-particle operation has been described. The process may be based on fixed-bed or on slurry-bed operation. It may be used, for example, for the production of hexane-1,6-diol by the reduction of an aqueous solution of adipic acid, and for the production of a mixture of hexane-1,6-diol, pentane-1,5-diol, and butane-1,4-diol by the reduction of a reaction mixture resulting from cyclohexane oxidation (CIO). 

The progress of the oxidation can be monitored by the disappearance of the diol using TLC (eluent, hexane ethyl acetate, 2 7). 

The efficacy of various normal and RP-TLC systems for the separation of the colour pigments of Capsicum annuum was compared. Neutral aluminium oxide, silica gel, diatomaceous earth, silica gel-diatomaceous earth 1 1, cellulose, cyano, diol- and amino modified silicas were employed as stationary phases for adsorption TLC. Polyamide and modified silica layers were used for RP-TLC as received, the other stationary phases were impregnated by overnight predevelopment in n-hexane - paraffin oil, 95 5 v/v. 

Hexane-1,6-diol was found to undergo an oxidation-cyclization process at elevated temperatures (250 °C) in the presence of a Cu-Cr catalyst supported on kieselguhr to yield 2,3,4,5-tetrahydrooxepin (68) (65JOC335). The final stage of the latter reaction involves a dehydration of the hemiacetal 2-hydroxyoxepane (75) as indicated in equation (38). An alternative type of base-induced cyclization (equation 39) involving intramolecular nucleophilic attack has been used in the synthesis of 4-ethoxycarbonyI-2,3,6,7-tetra-hydrooxepin (153) (73JOC1767). 

Disilyl ethers of bicyclo[2.2.0]hexane-l,4-diols were transformed to cyclohexane-1,4-diones by oxidation after hydrolysis in methanol to the diols, which can be isolated.100 Sodium periodate101-103 and molecular oxygen100,101,104 were used as oxidants. 

Carboxylic ookl cleavage of ecmicyelie and alicyclic epoxides is amply exemplified in the literature. Oxidation of methyleneoyolo-hexane with perforraic acid, for example, yields a 1,2-diol mono-formate, from which may be obtained 1-hydroxymethylcyclohexanol... 

Note. (1) These reaction conditions are used for the oxidation of decan-l-ol, hexane-1, 6-diol and oct-2-yn-l-ol. In the case of alcohols where acid-sensitive groups are also present (e.g. tetrahydropyranyl ethers), sodium acetate is added to buffer the reaction mixture alternatively pyridinium dichromate may be used.99... 

Chlor-5-ethyl-4-propyl- -2-oxid XII/2, 277 aus Phosphoroxychlorid und 2-Ethyl-hexan-1,3-diol XII/2, 278 2-Chlor-4-methyl- El, 183, 675 5-(Chlormethyl-5-methyl)-2-(4-nitro-phenoxy)- -2-sulfid E2, 698... 

The oxidation catalyst is believed to be ruthenium tetraoxide based on work by Engle,149 who showed that alkenes could be cleaved with stoichiometric amounts of ruthenium tetraoxide. Suitable solvents for the Ru/peracid systems are water and hexane, the alkene (if liquid) and aromatic compounds. Complex-ing solvents like dimethylformamide, acetonitrile and ethers, and the addition of nitrogen-complexing agents decrease the catalytic system s activity. It has also been found that the system has to be carefully buffered otherwise the yield of the resulting carboxylic acid drops drastically.150 The influence of various ruthenium compounds has also been studied, and generally most simple and complex ruthenium salts are active. The two exceptions are Ru-red and Ru-metal, which are both inferior to the others. Ruthenium to olefin molar ratios as low as 1/20000 will afford excellent cleavage yields (> 70%). vic-Diols are also... 

Cobalt(II) salts are effective catalysts for the oxidation of 1,2-glycols with molecular oxygen in aprotic polar solvents such as pyridine, 4-cyanopyridine, benzonitrile, DMF, anisole, chlorobenzene and sulfolane. Water, primary alcohols, fatty acids and nitrobenzene are not suitable as solvents. Aldehydic products are further oxidized under the reaction conditions. Thus, the oxidative fission of rram-cyclo-hexane-l,2-diol gives a mixture of aldehydes and acids. However, the method is of value in the preparation of carboxylic acids from vicinal diols on an industrial scale for example, decane-1,2-diol is cleaved by oxygen, catalyzed by cobalt(II) laurate, to produce nonanoic acid in 70% yield. ... 

The chiral octanediol in turn is converted into the corresponding cyclic sulfate by reaction with thionyl chloride and subsequent oxidation with sodium periodate and a catalytic amount of ruthenium(ni) chloride (0.1 mol%) (eq 2). In the final step, 1,2-diphosphinobenzene is lithiated by treatment with n-butyllithium (n-BuLi 2 equiv, 1.6 mol% in hexane) followed by the addition of the (3R,6R)-octane-3,6-diol cyclic sulfate (2 equiv) and a further addition of 2.2 equiv of n-BuLi. (5,5)-Ethyl-DuPHOS is obtained in a yield of over 70% [78% yield was described for the (R,R)-enantiomer by an analogous method ]. In addition to (5,5)-ethyl-DuPHOS, a variety of related bisphospholanes either linked by an ethylene bridge, or bearing other 2,5-alkyl substituents, or with opposite configuration have been prepared by this methodology. ... 

Dchydrocyclization of /t-hexane Hydrogenation of carbon dioxide Coupling of butane dehydrogenation and hydrogen oxidation Hydrogenation of cij,rra/w-butene-1,4-diol to c/5.rra/i5-butanediol Hydrogenation of 2-butyne-1,4-diol to ci5,/ran -butenediol... 

Normal phase systems consist of a polar adsorbent and a less polar mobile phase. Because these were the first available chromatographic systems they were named normal phase systems. They are for instance silica gels or other oxides in conjunction with a non-polar solvent such as heptane, hexane or some slightly polar solvents like dioxane. Semi-polar adsorbents such as cyano or diol phases can be operated in the normal phase mode as well. The combination of water and silica is not recommended due to the strong interaction between water and adsorbent. Furthermore silica is slightly soluble in water, which results in a shortened lifetime of the adsorbent. Normal phase systems are limited to organic solvents and thus the solutes have to be soluble in these solvents. 

The most convenient column for the separation of fullerenes and their oxides is the column packed by LiChrosorb Diol with eluent containing n-hexane and n-pentane. This... 

Figure 3. Separation of fullerenes and fuUerene oxides on n Bondapak C 18 from i-propanol-n-hexane (20 80) eluent (column 300x4 mm, w = 0.4 ml/min) (a) and on LiChro-sorb Diol from n-hexane - n-pentane (80 20) eluent (column 250x4.6 mm, w = 0.2 ml/min)...

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