From diols hydrogenation

Substrate (R—CO—CHj—CO—R) R Proportion of diastereomers (%) in the hydrogenation product Isolation of (R,R)-diol from the hydrogenation product ... 

Some reaction parameters were therefore changed in order to study the influence of the different steps on the obtained yields. Thus the catalyst concentration was lowered and the inversion could partly be separated from the hydrogenation and the hydrogenolysis (part B). This resulted in a better yield in 1,2-propane diol (24% after 4 hours). Decreasing the catalyst concentration... 

The process scheme is not complicated and yields on olefin feed are good. The major byproduct is paraffin from olefin hydrogenation in the reactor system. However paraffin make is low. Also some olefin remains unconverted, some dimer is formed, and traces of other byproducts are made. These include acetals, esters and diols. These other losses (excluding paraffins) total less than 5%. 

Currently the global production of hexamethylenediamine exceeds 1.2 Mt/a and production (e.g. ICI, BASF and Rhone-Poulenc in Europe) is based on the hydrogenation of adiponitrile, largely obtained by catalytic addition of HCN to butadiene. Celanese produced hexamethylenediamine by reaction of ammonia with hexane-1,6-diol, coming from the hydrogenation of adipic acid. However, production by this method was abandoned in 1984. 

Although a similar rebound process may occur in the cleavage of 1,2-diols [via the sequential abstraction of hydrogen atoms from carbon centers by the ClaFeVfO) reactive intermediate], a more plausible process is the concerted removal of the two diol hydrogen atoms via intermediate 4 of Scheme 4-3 to generate a dioxetane intermediate, followed by a facile homolytic cleavage to the observed products [Eq. (4-37)]. 

Near infrared studies on a solution of chloral hydrate show the existence of a labile equilibrium between the gem-diol and a dimolecular 1 1 complex of the aldehyde and water. It is thought that the gem-diol structure results from the electronic effect of the halogens transmitted through the molecule, rather than from intramolecular hydrogen bonding between the halogens and the hydroxyl hydrogens. 

Bromine sodium hydrogen carbonate Oxidations with halogen/hexamethylphosphoramide Oxo compds. from alcohols Hydroxyketones from diols Retention of prim, alcohol groups... 

The high melting point of polyamides derives from interchain hydrogen bonding. Polyurethanes are prepared from diisocyanates and diols. 

During the development of the one-pot reaction sequence for the case in Fig. 8.40, it is important to avoid diol formation from over-hydrogenation, thus the loading of hydrogenation catalysts should be optimized. Suppression of the consecutive hydrogenation to diols is essential in the one-pot approach where, in the presence of an enzyme, lipase-catalyzed acetylation of the isomeric alcohols would result in undesired mixtures of acetylated products. 

Prepared by heating ammonium mucate, or from butyne-l,4-diol and ammonia in the presence of an alumina catalyst. The pyrrole molecule is aromatic in character. It is not basic and the imino-hydrogen atom can be replaced by potassium. Many pyrrole derivatives occur naturally, e.g. proline, indican, haem and chlorophyll. 

In a 500 ml. three-necked flask, equipped with a mechanical stirrer, thermometer and dropping funnel, place 300 ml. of 88-90 per cent, formic acid and add 70 ml. of 30 per cent, hydrogen peroxide. Then introduce slowly 41 g. (51 ml.) of freshly distilled cyclohexene (Section 111,12) over a period of 20-30 minutes maintain the temperature of the reaction mixture between 40° and 45° by cooling with an ice bath and controlling the rate of addition. Keep the reaction mixture at 40° for 1 hour after all the cyclohexene has been added and then allow to stand overnight at room temperature. Remove most of the formic acid and water by distillation from a water bath under reduced pressure. Add an ice-cold solution of 40 g. of sodium hydroxide in 75 ml. of water in small portions to the residual mixture of the diol and its formate take care that the tempera... 

The 7, i5-unsaturated alcohol 99 is cyclized to 2-vinyl-5-phenyltetrahydro-furan (100) by exo cyclization in aqueous alcohol[124]. On the other hand, the dihydropyran 101 is formed by endo cyclization from a 7, (5-unsaturated alcohol substituted by two methyl groups at the i5-position. The direction of elimination of /3-hydrogen to give either enol ethers or allylic ethers can be controlled by using DMSO as a solvent and utilized in the synthesis of the tetronomycin precursor 102[125], The oxidation of the optically active 3-alkene-l,2-diol 103 affords the 2,5-dihydrofuran 104 in high ee. It should be noted that /3-OH is eliminated rather than /3-H at the end of the reac-tion[126]. 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

Much more important is the hydrogenation product of butynediol, 1,4-butanediol [110-63-4]. The intermediate 2-butene-l,4-diol is also commercially available but has found few uses. 1,4-Butanediol, however, is used widely in polyurethanes and is of increasing interest for the preparation of thermoplastic polyesters, especially the terephthalate. Butanediol is also used as the starting material for a further series of chemicals including tetrahydrofuran, y-butyrolactone, 2-pyrrohdinone, A/-methylpyrrohdinone, and A/-vinylpyrrohdinone (see Acetylene-DERIVED chemicals). The 1,4-butanediol market essentially represents the only growing demand for acetylene as a feedstock. This demand is reported (34) as growing from 54,000 metric tons of acetylene in 1989 to a projected level of 88,000 metric tons in 1994. 

Reduction. These hydroxybenzaldehydes can be reduced by catalytic hydrogenation over palladium or platinium to yield the corresponding hydroxybenzyl alcohols, but the electrolytic reduction in an alkaline medium gives the coupling product l,2-bis(4-hydroxyphenyl)ethane-l,2-diol in very good yield from 4-hydroxybenzaldehyde (49—51). 

Functional Olefin Hydroformylation. There has been widespread academic (18,19) and industrial (20) interest in functional olefin hydroformylation as a route to polyfiinctional molecules, eg, diols. There are two commercially practiced oxo processes employing functionalized olefin feedstocks. Akyl alcohol hydroformylation is carried out by Arco under Hcense from Kuraray (20,21). 1,4-Butanediol [110-63 ] is produced by successive hydroformylation of aHyl alcohol [107-18-6] aqueous extraction of the intermediate 2-hydroxytetrahydrofuran, and subsequent hydrogenation. 

Diol Components. Ethylene glycol (ethane 1,2-diol) is made from ethylene by direct air oxidation to ethylene oxide and ring opening with water to give 1,2-diol (40) (see Glycols). Butane-1,4-diol is stiU made by the Reppe process acetylene reacts with formaldehyde in the presence of catalyst to give 2-butyne-l,4-diol which is hydrogenated to butanediol (see Acetylene-DERIVED chemicals). The ethynylation step depends on a special cuprous... 

Cyclohexanedimethanol (47) starts from dimethyl terephthalate. The aromatic ring is hydrogenated in methanol to dimethyl cyclohexane-l,4-dicarboxylate (hexahydro-DMT) and the ester groups are further reduced under high pressure to the bis primary alcohol, usually as a 68/32 mixture of trans and cis forms. The mixed diol is a sticky low melting soHd, mp 45—50°C. It is of interest that waste PET polymer maybe direcdy hydrogenated in methanol to cyclohexanedimethanol (48). 

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