Diol isomers

As noted at the end of Section 7.8, the prefixes cis- and trans- would be ambiguous when naming the diols derived from 1-methylcyclohexene because the ring has three substituents. Instead, a reference substituent r is chosen and other substituents are either cis (c) or trans (f) to that reference. For the two l-methyl-l,2-cyc ohexanediol isomers, the -OH group at Cl is the reference (r-1), and the -OH at C2 is either cis (c-2) or trans (t-2) to that reference. Thus, the diol isomer derived by cis hydroxylation is named l-methyl-r-l,c-2-cyc ohexanediol, and the isomer derived by trans hydroxylation is named l-methyl-r-l,t-2-cyclohexanediol. 

Rose oxide is usually prepared from citronellol which can be converted into a mixture of two allyl hydroperoxides (e.g., by photosensitized oxidation with oxygen). Reduction of the hydroperoxides with sodium sulfite yields the corresponding diols [183]. Treatment with dilute sulfuric acid results in allylic rearrangement and spontaneous cyclization of one of the isomers a mixture of diastereoisomeric rose oxides is thus formed. The unreacted diol isomer is separated by distillation. (—)-Citronellol as the starting material yields approximately a 1 1 mixture of (—)-cis- and (—)-tra s-rose oxide. 

With alkenes and peroxides room temperature epoxidation can be performed, the selectivity with respect to ring-openend products being dependent on solvent and hydroperoxide nature.[96] With organic peroxides the epoxide selectivity is high, while with HOOH in acetone high diol selectivity is evident with the cis/trans diol isomer ratio at its equilibrium value. 

Fig. 4.5 Extent of hydrolysis of glycoside of different volatile compounds during MLF with four strains of malolactic bacteria (MLB). Values are calculated as a percentage ratio between the concentration of glycosides in MLF samples and in a non-MLF control. Sum of 1-hexanol, trans- and CM-3-hexenol, trans- and c/i-2-hexenol sum of isoamyl alcohols, heptanol, and 4-hydroxy-4-methyl-2-pentanol sum of benzyl alcohol and 2-phenylethanol sum of vanillin and benzaldehyde sum of 4-vinylphenol and 4-vinylguaiacol sum of Unalool and a-terpineol sum of nerol and geraniol sum of cis- and rrani-linalool oxides (pyranic and furanic) sum of 3,7-dimethyl-l,5-octadien-3,7-diol and the two 2,7-dimethyl-2,7-octadien-l,6-diol isomers (from Ugliano and Moio 2006, reproduced with permission)...

The configuration of the major 1,4-diol isomer from the lithium reduction of 4-hydroxy-2-t-butyl-3-methyl-2-cyclopentenone has been determined " and shows the ring to be almost half-chair in form with a binary axis passing through C-3 and bisecting the C-1 and C-5 segment. 

Diastereoselective osmylation and hydroboration of, y-unsaturated (V,(V-diisoprop-ylamides (100)-(1 2) have been reported to occur with useful diastereofacial selectivity (Scheme 11). The major diol isomer from (E)-alkenes (100) and (101), in the presence of TMEDA at -78 °C, corresponds to the facial preference shown in transition-state model (103) [(100) gave an 11 1 preference at -78 °C (101) afforded the same ratio at —78 °C, and 6 1 at room temperature], while the opposite preference for (104) is observed with the (Z)-alkene (102) (>20 1 at —78°C and 7 1 at room temperature). Hydroboration with 9-BBN does not show this inversion of diastereofacial selectivity for the (Z)-alkene all of the results correspond to the usual preference for a transition state such as (105). ... 

D-t/ reo-butane-2,3-diol L-i/ireo-butane-2,3-diol 8-30, butane-2,3-diol isomers... 

Viji unya also studied the effect of some diol isomers as the liquid fillers in mixed-matrix membranes for gas separation. They incorporated 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol liquid fillers into silicone rubber coating on top of the porous polysulfone support membrane. Similar to PEG liquid filler, it was found that 1,2-butanediol and 2,3-butanediol could improve propylene over propane selectivity. However, the selectivity of propylene over propane was not enhanced when 1,3-butanediol and 1,4-butanediol were added to silicone rubber. In PEG, the hydroxyl group is attached to each carbon atom on carbon backbones. A portion of 1,2- and 2,3-butanediol molecules are similar to PEG in which the hydroxyl groups are attached to the adjacent carbon atoms. In contrast, the hydroxyl groups in 1,3- and 1,4-butanediol molecules are not attached to the adjacent carbon atoms. Therefore, it was proposed that the position of hydroxyl groups of the butanediols plays an important role for the improvement of propylene over propane selectivity. 

A highly diastereoselective alkcnylation of c/s-4-cyclopentene-l,3>diols has been achieved with 0-protected (Z)-l-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The ( )-isomers yielded 1 1 mixtures of diastcrcomcric products. The (Z)-alkenylpalladium intermediate is thought to undergo sy/i-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. 

Butenediol. 2-Butene-l,4-diol [110-64-5] is the only commercially available olefinic diol with primary hydroxyl groups. The commercial product consists almost entirely of the cis isomer. 

Ma.nufa.cture. Butenediol is manufactured by partial hydrogenation of butynediol. Although suitable conditions can lead to either cis or trans isomers (111), the commercial product contains almost exclusively iVj -2-butene-l,4-diol Trans isomer, available at one time by hydrolysis of l,4-dichloro-2-butene, is unsuitable for the major uses of butenediol involving Diels-Alder reactions. The Hquid-phase heat of hydrogenation of butynediol to butenediol is 156 kj/mol (37.28 kcal/mol) (112). 

Albright Wilson s Vircol 82 is a diol mixture obtained by the reaction of propylene oxide and dibutyl acid pyrophosphate (112). The neutral Hquid has an OH number of 205 mg KOH/g and contains 11.3% phosphoms corresponding to the formula shown where x y = 3.4. The product is a mixture of isomers. 

Cydohexanedimethanol, 1,4- dim ethyl o1 cycl oh exa n e, or 1,4-bis (hydroxymethyl) cyclohexane (8), is a white, waxy soHd. The commercial product consists of a mixture of cis and trans isomers (6). This diol is used in the manufacture of polyester fibers (qv) (64), high performance coatings, and unsaturated polyester molding and laminating resins (5). 

Properties of PGT. Typical properties of PCT are shown in Tables 5 and 6 (154). Table 5 shows the standard grades and Table 6 the PR grades. This material is in effect a copolymer of terephthaUc acid with two diols, the cis and trans forms of cyclohexanedimethanol. These two isomers do not form a eutectic copolymer with a minimum melting point, but instead the melting point rises monotonically between the two values of the pure... 

Other minor raw materials are used for specific needs. Eumaric acid [110-17-8] the geometric isomer of maleic acid, is selected to maximize thermal or corrosion performance and is the sole acid esterified with bisphenol A diol derivatives to obtain optimum polymer performance. CycloaUphatics such as hydrogenated bisphenol A (HBPA) and cyclohexanedimethanol (CHDM) are used in selective formulations for electrical apphcations. TetrahydrophthaUc anhydride [85-43-8] (THPA) can be used to improve resiUence and impart useful air-drying properties to polyester resins intended for coating or lining apphcations. 

The 1,4-isomer has been similarly generated from terephthalonitdle [623-26-7] (56) using a mixed Pd/Ru catalyst and ammonia plus solvent at 125 °C and 10 MPa (100 atm). It is also potentially derived (57) from terephthaUc acid [100-21-0] by amination of 1,4-cyclohexanedimethanol (30) [105-08-8], Endocyclization, however, competes favorably and results in formation of the secondary amine (31) 3-a2abicyclo[3.2.2]nonane [283-24-9] upon diol reaction with ammonia over dehydration and dehydrogenation catalysts (58) ... 

Methylenedi(cyclohexyhsocyanate) (45) [5124-30-1] (MDCHl, Desmodur W) is the dominant derivative of MDCHA and is used in light-stable urethanes. Polyurethane physical properties are dependent on the diamine geometric isomer composition used for the derivative diisocyanate which reacts with diol (87). 

Until the mid-1960s, phenylenediamines were used primarily for oxidative purposes the para isomer was of major importance. Since then, the use of phenylenediamines to manufacture polymers has far exceeded their use for oxidative purposes. The y -phenylenediamines, (2,4 and 2,6)-toluenediamine, are widely used for the manufacture of polyurethanes. Phenylenediamines are dihinctional and react with other dihinctional compounds, such as dianhydrides, diacyl chlorides, dicarboxyHc acids, and disulfonyl chlorides to give polyamides. Phenylenediamines also give polymers with epoxides, diols, diacetals. 

CitroneUal can also be converted to the ds- [92471-23-3] (88) and / 3 -/)-menthane-3,8-diol [91739-72-9] (89) by reaction with dilute acids (176,177). The glycol mixture can be readily purified by distillation and the two isomers easily separated. The glycols are usehil as insect repellents (qv) and are especially effective against mosquitos (178). Derivatives of the glycols have been prepared and are usehil as insecticides and plant growth regulators (179). 

Cyclopentadiene has also been oxidized by singlet oxygen to 4,5-epoxypenten-2-al-l, cis and trans isomers. These compounds and their hydrogenated diol products are claimed as useful intermediates as cross-linking agents, and in the production of pesticides and perfumes (34). 

BzOOBz, Ph3P, CH2CI2, 1 h, It, =80% yield. When these conditions are applied to unsymmetrical 1,2-diols, the benzoate of the kinetically and thermodynamically less stable isomer is formed. 

The following ortho esters have been prepared to protect the diols of nucleosides. They are readily hydrolyzed with mild acjd to afford monoester derivatives, generally as a mixture of positional isomers. 

DL-erytAro-Dihydrosphingosine (dl-erytAro-2-aniinooctadecan>l,3-diol) [3102-56-5] M 301.5, m 85-86 , 85-87 , pK ,t -- 8.8. Purified by recrystn from pet ether-EtOAc or CHCI3. The ( )-N-dichloroacetyl derivative has m 142-144° (from MeOH). [Shapiro et al. J Am Chem Soc 80 2170 1958 Shapiro and Sheradsky J Org Chem 28 2157 796i.] The D-isomer crystallises from pet ether-Et20 and has m... 

Stoddart and his coworkers have reported syntheses of the trans-syn-trans and the trans-anti-trans isomers of dicyclohexano-18-crown-6 The synthesis of these two compounds from trans-l,2-cyclohexanediol was accomplished in two stages. First, the diols were temporarily linked on one side by formation of the formal, and this was treated with diethylene glycol ditosylate and sodium hydride to form the hemi-crown formal. Removal of the formal protecting group, followed by a second cychzation completed the synthesis. The synthesis of the trans-anti-trans compound is illustrated below m Eq (3 12) and the structures of the five possible stereoisomers are shown as structures 1—5. 

Regioselectivity in opening of a-functionalized epoxides by treatment with trimethylamine dihydrofluoride has been observed. Thus, cw-isophorol epoxide gives exclusively 3-fluoro-l,2-diol, whereas from the trans isomer, 2-fluoro-l,3-diol is obtained as the main product together with 3-methylenecyclohexane-l,2-diol. This behavior has been discussed m terms of the influence of a-substituents on the transition state conformations [7 J] (equations 11 and 12). 

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

PerfluoroaUcenes are converted to vicinal diols when no fluonne atom is present at the double bond Configurational isomers of perfluoroalkenes [29] (equations 20 and 21) are oxidized stereospecifically Perfluorbicyclo[4 3 0]non-1(6) ene gives the corresponding 1,6 diol m a 24% yield upon oxidation with potassium permanganate at 18 °C for 1 h [29]... 

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