Dihydroxy compounds

By the addition of hydrogen peroxide to a solution of 4-methylphenol in antimony pentafluoride/hydrogen fluoride (2 5) at -40°C and reaction with stirring during 30 mins., 4-methylresorcinol was formed in 78% yield (ref. 14). 

5-Methylresorcinol monomethylether (orcinol monomethylether) has been synthesised in 71% yield from 3-methylcyclobut-2-enone (2.5 moles) and 2-methoxyacetylene (1-1.2 moles) in the presence of 2,4,6-tri-tert-butylphenol (1.1 moles) by heating the mixture in a sealed tube at 80°C for 26 hours followed by treatment of the crude product with hot 10% methanolic potassium hydroxide during several hours (ref. 15). 

The 5-phenyl analogue has been obtained by a type of Homer-Emmons reaction. 4-Methoxy-6-phenyl-2-pyrone in tetrahydrofuran was added at -10 C to dimethyl methylphosphonate in tetrahydrofuran previously treated at -10°C with n-butyllithium in hexane and reacted for 30 mins. Further butyllithium was introduced and after reaction during 1 hour at ambient temperature and work-up by acidification, 5-phenylresorcinol monomethylether was isolated in 88% yield (ref.16). 

4-(2-hydroxyethyl)resorcinol has been prepared by the Michael addition of the carbanion from a-phenylsulphinyl-y-butyrolactone with methyl vinyl ketone (but-1-en-3-one) followed by thermal treatment of the intermediate adduct (ref. 17). 

Earlier syntheses had employed PhSOCHjCOsMe (A) and RCH=CHCOMe, and PhSOCHjCOMe (B) with RCH=CHC02Me, (R = alkyl or Ph) (ref.18). 

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Reduction, (a) By sulphurous acid. Benzoquinone, /> toluquinone, 1,2-naphthoquinone are readily reduced by SOj ultimately to the dihydroxy-compound. Thus benzoquinone gives colourless hydro-quinone or quinol, />-C2H4fOH)2. 

The general syntheses of alkenes (p. 28 — 44) and 1,2-dihydroxy compounds (p. 50—54 and 123 — 132) are not repeated here. But there is an important chiral pool" for chiral 1,2-disubstituted compounds, namely a-amino acids. 

Linear polyethers derived from three or more molecules of aliphatic dihydroxy compounds, particularly when the chain length exceeds ten units, are most conveniently named by open-chain replacement nomenclature. For example, CH3CH2—O—CH2CH2—O—CH2CH3 could be 3,6-dioxaoctane or (2-ethoxy)ethoxyethane. 

As a variation on the base-catalyzed nucleopbilic displacement chemistry described, polysulfones and other polyarylethers have been prepared by cuprous chloride-catalyzed polycondensation of aromatic dihydroxy compounds with aromatic dibromo compounds. The advantage of this route is that it does not require that the aromatic dibromo compound be activated by an electron-withdrawing group such as the sulfone group. Details of this polymerization method, known as the Ullmaim synthesis, have been described (8). 

Antimony pentoxide also reacts with a variety of dihydroxy compounds. Thus pyrocatechol yields a crystalline substance ia which three molecules of the diol are associated with one atom of antimony (52). The configuration of this substance has not been estabUshed, but the foUowiag stmcture seems reasonable ... 

Transesterification has become a convenient method for synthesi2ing high alkyl, aryl, or alkyl aryl carbonates. Fiber- and film-forming polycarbonates are produced by transesterifying dialkyl, dicycloalkyl, or diaryl carbonates with alkyl, cycloalkyl, or aryl dihydroxy compounds (62). 

Cleavage of an alkenoic acid can be carried out with permanganate, a permanganate—periodate mixture, periodate or with nitric acid, dichromate, ozone, or, if the unsaturation is first converted to a dihydroxy compound, lead tetraacetate (71,73). Oxidative ozonolysis is a process for the manufacture of azelaic acid [123-99-9] and pelargonic acid (74). 

Polycarbonates. Polyarjiates are aromatic polyesters commonly prepared from aromatic dicarboxylic acids and diphenols. One of the most important polyarylates is polycarbonate, a polyester of carbonic acid. Polycarbonate composite is extensively used in the automotive industry because the resin is a tough, corrosion-resistant material. Polycarbonates (qv) can be prepared from aUphatic or aromatic materials by two routes reaction of a dihydroxy compound with phosgene accompanied by Hberation ofHCl(eq. 5) ... 

With malonic acid as the C3 fragment in the presence of acetic anhydride, 6-substituted 5,7-dihydroxy compounds are obtained (64JOC219,61M1184), whilst the 6-IV-lithio derivative of a uracil (251) reacted with a ketenimine to give the 7-t-butylamino compound (252) (77JOC221). 

Potential 2,5-dihydroxy compounds (185) exist in the dicarbonyl forms (186). Succinic anhydride (186 Z = O) on silylation is converted into 2,5-bis(trimethylsilyloxy)furan (187) the latter compound readily participates in Diels-Alder addition reactions (80TL3423). Reaction of thiosuccinic anhydride (186 Z = S) with the triphenylphosphorane Et02CH=PPh3 gives a product which exists in the aromatic form (188) (75LA1967). 

An alternative technique is that of condensation polymerisation. A simple example of this is seen in the manufacture of linear polyesters. Here a dibasic acid is reacted with a dihydroxy compound, e.g. a glycol (Figure 2.5). 

Reduction in compression set began to be achieved in the late 1960s when it was found that tropolene and phenanthroline not only accelerated amine cures but were also effective with certain bisnucleophiles such as resorcinol, hydroquinone and bis-phenol AF. In due course even better results were obtained with quaternary ammonium or phosphonium salts being used in conjunction with aromatic dihydroxy compounds. 

Carothers also produced a number of aliphatic linear polyesters but these did not fulfil his requirements for a fibre-forming polymer which were eventually met by the polyamide, nylon 66. As a consequence the polyesters were discarded by Carothers. However, in 1941 Whinfield and Dickson working at the Calico Printers Association in England announced the discovery of a fibre from poly(ethylene terephthalate). Prompted by the success of such a polymer, Farbenfabriken Bayer initiated a programme in search of other useful polymers containing aromatic rings in the main chain. Carbonic acid derivatives were reacted with many dihydroxy compounds and one of these, bis-phenol A, produced a polymer of immediate promise. 

Ester exchange of dihydroxy compounds with diesters of carbonic acid and monofunctional aromatic or aliphatic hydroxy compounds. 

Ester exchange of bis-alkyl or bis-aryl carbonates of dihydroxy compounds with themselves or with other dihydroxy compound. 

Reaction of dihydroxy compounds with phosgene in the presence of acid acceptors. 

The tri/luorovinyloxy group is cleaved by potassium persulfate [37J The pnmanly formed dihydroxy compound undergoes spontaneous hydrolysis with the formation of carboxylic acid (equation 29)... 

Dichloroquinazolines have been prepared from the corresponding 2,4-dihydroxy compounds by heating for a few hours with phosphorus oxychloride in the presence of dimethyl aniline or phosphorus penta-chloride. These are more stable than the monochloro compounds and can be distilled in vacuum without appreciable decomposition. 

Fusion of 4-hydroxyquinazoIine with phosphorus pentasulfide yields 4-mercaptoquinazoline and, similarly, substituted 2,4-dimercapto-quinazolines have been obtained from the corresponding dihydroxy compounds. The greater reactivity of the 4-mercapto as compared with the 2-mercapto group has permitted the preparation of 4-amino-2-mercaptoquinazolines (see 7a). 

Occasionally it happens that the oxo compound, produced by oxidation, forms a hydrate which is further oxidized to a dihydroxy compound. Attention must be given to the possibility (so far unreported) that when the hydrated species is in equilibrium with a trace of the ring-opened structure a sufficiently fast oxidation rate of the amino-aldehyde (i.e. the acyclic structure) could lead to the incorrect conclusion that the original material was not cyclic. 

Aromatic ortho-dihydroxy compounds as reagents for inorganic analysis. B. W. Bundesinsky and K. E. Curtis, Chelates Anal. Chem., 1976,5,163-292(398). 

L. P. Kuhn pointed out that, if hydroxyl groups of an a-dihydroxy compound are sufficiently close, they will form an internal hydrogen-bond. 

Several studies, however, conclusively showed that the intensity of the sweet taste depends strongly upon the number of hydroxyl groups in the A-ring. - - For example, compound 85 and its sodium salt, which have only one hydroxyl group in the A-ring, are less sweet than the 2,6-dihydroxy compound. Furthermore, there is also a requirement for an orrto-hydroxy ketone system in ring A, as compound 86 is tasteless, and because it had already been shown that the alkoxy-hydroxy substituents on ring B are also... 

When 1,4-dihydroxy compounds are produced by monooxygenation, these are degraded by the gentisate pathway (Figure 3.13) mediated by gentisate dioxygenase (Wergath et al. 1998). 

Hydroxylation to 1,4-dihydroxy compounds may also activate the ring to oxidative fission. This is illustrated by the following examples of the gentisate pathway ... 

After formation of the 1,2-dihydroxy compounds, ring fission is mediated by 1 2 (intradiol fission) or 2 3 (extradiol and distal fission) dioxygenases. There are, however, important variations in the pathways used by various groups of microorganisms ... 

Both 2-hydroxy- and 3-hydroxypyridine are hydroxylated to 2,5-dihydroxypyridine by strains of Achromobacter sp. (Houghton and Cain 1972). These metabolites are probably, however, formed by different reactions whereas 3-hydroxypyridine behaves as a true pyridine, addition of H2O across the Cg Nj bond would produce the 2,5-dihydroxy compound 2-hydroxypyridine is a cyclic amide and hydroxylation apparently occurs at the diagonal position. The degradation of 4-hydroxypyridine is also initiated by hydroxylation and is followed by dioxygenation before ring fission (Figure 10.12) (Watson et al. 1974). 

Polycarbonates have also been studied recently with regard to chemical heterogeneity. Polycarbonates are polycondensation products of phosgene and aliphatic or aromatic dihydroxy compounds. 

The monohydrate, possibly the gem-dihydroxy compound and an ac/ -nitro salt, is an impact-sensitive solid and must be carefully handled with precautions. 

Although 7,14-dihydroxy-6H,13H-pyrazino[l,2- 4,5-,T]bisindole-6,13-dione can jn pr ncipie exist in two tautomeric forms of the dihydroxy compound 39 and the diketo form 40, only the dihydroxy is observed <2003OBC3396>. Presumably this is due to the enolizable 1,3-dicarbonyl moieties and the formation of the indole ring, therefore leading to aromaticity and a net overall stabilization. 

Lekishvili N.G., Katsitadze M.G., Nakaidze L.I., Khananashvili L.M. Some Kinetically Regularities of Polymerization Condensation Reaction of Organocyclosilazanes with Spacial Groups at Silicon Atoms with Aromatic Dihydroxy compounds. Bulletin of the Academy of Sciences of Georgia. Series of Chemistry. 152, 3 529-531 (1995) (Rus.). 

In 1997, Laux and Krause showed that ruthenium(III) chloride can catalyze the oxidation of allenes 48 to a,a -dihydroxy ketones 49 [17]. They used sodium periodate as a stoichiometric oxidant and obtained the products in moderate to good yields, probably owing to overoxidation (Scheme 17.16). The dihydroxy compound was formed with high diastereomeric excess in one example when a chiral allene was oxidized. 

It is well to note at this point that the dihydroxy compound is the first identifiable compound from the photolysis and photo-oxidation reactions that actually has any color. The lack of other identifiable color compounds and also some preliminary experiments lead to a proposal [9] that the oxidation of the dihydroxy compound could actually continue on to give a quinone (Scheme 18.5, top). Given the ease of oxidation of hydroquinone compounds, this would seem to be a reasonable proposal. In this preliminary report where an orange-red solid was initially observed it was speculated that the color owed itself to a quinone compound as shown. This would add significantly to compounds that actually could be the color bodies formed upon weathering exposure. 

Unsaturated polyesters are prepared through a classical esterification process. Typically, a dihydroxy compound, or mixtures of dihydroxy compounds, are treated with maleic anhydride and/or together with other dicarboxylic acids such as aromatic or aliphatic dicarboxylic acids under elevated temperature to remove the water produced during esterification process. Although various catalysts will catalyze this esterification reaction, there is enough carboxylic acid in the mixture so that it is not necessary to add extra catalyst. 

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