Dihydric phenols Production

Originally from China, Rhus vernicefera has been under cultivation in Japan since the sixth century AD. The latex is collected in the same way as the rubber plant Hevea brasiliensis. The product is known as urushiol, which consists mostly of dihydric phenols of structures (Fig. 6) and is used as lacquers. 

New phenolic phosphites prepared from dihydric phenols and phosphorus halides prevent degradation of polypropylene by heat, oxidation, processing, and ultraviolet radiation. These products are active and synergistic with dithiopropionate esters. They seem to function as both free radical scavengers and peroxide decomposers. 

It is clear from the proposed mechanism that the initial step will be facilitated by the presence of a second hydroxyl group in the phenol, oriented meta to the first. In view of the importance of polyphenolic molecules in natural product chemistry, this synthesis takes on a special significance. Thus, the reaction of dihydric phenols with citral (65) has been used to synthesize a diverse range of natural products. However, such compounds can, and in some cases do, give rise to a mixture of isomeric products. Olivetol (64), for instance, yields a mixture of mono- and bis-chromenes of which cannabichromene (66) is a significant component (71JCS(C)796). On the other hand, the phenol (67) affords a h igh yield of isoevodionol (68) on reaction with 4,4-dimethoxy-2-methylbutan-2-ol (71JCS(C)8U). 

This is one of the most widely distributed plants cultivated to obtain cashew nut. The phenolic lipid is only a by-product known as cashew nut shell liquid (CNSL). The nut, attached to the base of the cashew nut apple consists of an ivory-colored kernel covered by a thin brown membrane (testa) and enclosed by an outer porous shell, the mesocarp which is about 3 mm thick with a honey-comb structure where the reddish brown liquid (CNSL) is stored [91]. The major components of CNSL are a phenolic acid, anacardic acid, a dihydric phenol, cardol with traces of mono hydric phenol, cardanol, and 2-methyl cardol [92-95]. 

A generally applicable reaction is that due to Elbs302 in which phenols are oxidized to dihydric phenols by 1 mole of peroxydisulfuric acid in an alkaline medium. The second hydroxyl group enters the para-position to the first. A para-substituted monohydric phenol gives good yields of ortho-oxidation products on oxidation with 3 moles of H2S208. 

Analysis of the oxidation products of chain-breaking antioxidants from the group of dihydric phenols reveal that quinoid compounds are involved in the mechanism of their action. Due to the formation of benzoquinones and hydroxybenzoquinones, the dihydric phenols are staining antioxidants. This fact reduces the technical importance of this in other ways very interesting group of antioxidants. 

In 1865 just prior to Kekule s synthesis of phenol, Joseph Lister (1827-1912) was experimenting with carbolic acid as an aid to antiseptic surgery which he had pioneered. A mixture of crystallised carbolic acid and shellac (lac plaster) was employed in the finally adopted mode of application. The requirement of phenol for the manufacture of picric acid during the Boer war and other uses resulted in a demand which soon outstripped the resources of phenol/cresols available from coal distillation. Synthetic phenol thus became a potentially important intermediate. The lengthy processing involved in the separation of phenol and the isomeric cresols led to the desirability for specific syntheses. In 1978 of the world production of phenol only 3% came from coal sources by extraction of the mixed phenols (about 1.5% in coal tar) with 10% sodium hydroxide, acidification with carbon dbxide and separation. Phenolic compounds are also formed during catalytic cracking processes in the petroleum industry. There are historically six industriai processes for the production of synthetic phenol, variously from benzene and toluene, some of which are also applicable to the cresols and the dihydric phenols. 

The dihydric phenols are speciality products widely used industrially and commercially. Hydroquinone and its relative, 4-methylaminophenol (metol) are the main chemicals used for development in black and white photography. Butylated hydroxyanisole, (BHA) mainly 2,6-di-tert-butyl-4-methoxyphenol (5), an important food antioxidant is synthesised from 2,4,6-tri-t-butylphenol by reaction in methanolic solution with chlorine to give 2,4,6-tri-t-butyl-4-methoxy-... 

Catechol is also employed for the industrial antioxidant 4-tert-butylcatechol, and its monomethyl ether, guaiacol is used for the production of vanillin (10). This account is by no means a complete summary of the applications of the dihydric phenols more of which have been listed elsewhere (ref. 38). 

In conclusion it can be seen that the production of phenol, 4-methylphenol and the isomeric dihydric phenols, with the exception of catechol, is dominated by hydroperoxidation technology. The comprehensiveness and elegance of this methodology rests partly upon the simultaneous recovery of acetone and in the dihydric series upon the thermal equilibration step to obtain the stable but... 

An inherent problem in the usage of phenolic lipids, particularly in surface coatings, is the discolouration which can impair products. Apart from colourants arising from the solvent action of CNSL on the shell in the industrial process, the dihydric phenols In CNSL notably the minor component 2-methylcardol (ref. 200) more than cardol appear to be the cause of this deterioration rather than the monohydric member, cardanol. The usage of purer cardanol, or the less unsaturated material by semi-hydrogenation or chemical reduction, as well as the Incorporation of an antioxidant are methods for colour stabilisation (ref. 277). Antioxidant applications and pharmaceutical uses of CNSL and its component phenols are referred to in the next section. 

O-Alkyl phosphorotrithioate salts are converted by treatment with hydrogen chloride and a dihydric phenol into the mixed esters (52). Structure (53) has been proposed for the product from reaction of phosphorus pentasulphide with the thiophen derivative (54). Studies on the... 

Resorcinol (a dihydric phenol) when reacted with acetonitrile (or methyl cyanide) in the presence of anhydrous zinc chloride in an ethereal medium at 0°C produces the chlorozincate of an Tmine Salt . The resulting intermediate on subjecting to hydrolysis at almost 100°C knocks out a mole of NH Cl with the production of resacetophenone. 

A 0iile the carbonate method for preparing the polymers is simple and convenient, in some cases products of higher molecular weight can be obtained by the alkali metal hydroxide method. In the alkali metal hydroxide method, a double alkali metal salt of a dihydric phenol is reacted with a dihalobenzenoid compound. 

Polycondensation of Phosphoryl Dihalides with Diols. Poly(arylene aryl phosphate)s can be made stepwise by first preparing a phenyl phosphorodichlori-date which reacts with a dihydric phenol, or in one step by the reaction of phosphorus oxychloride with a mixture of monohydric and dihydric phenols. Depending on the reactant ratio, the products can be oligomers or high molecular weight thermoplastic or thermoset polymers (129). 

Other products that may be epoxidized in this way include dihydric and trihydric phenols, aliphatic polyols such as glycerol, and simple alcohols such as butanol or alyl alcohol. These products, especially the monofunctional glycidyl ethers, are used at relatively low percentages to reduce the viscosity of formulations containing DGEBA resins. In this way, they act as reactive diluents. 

The phenolic lipids occur in many different botanical families, notably in the Anacardiaceae, and they exist in tropical, sub-tropical, temperate climates in certain trees, shrubs and plants. In addition they are found in some bacterial and antibiotic sources and in certain insects. As benzenoid derivatives they are conveniently. although perhaps artificially, grouped for chemical purposes into phenolic acids, polyhydric, dihydric and monohydric phenols. Tables 13.1, 13.2 and 13.3 and the collections of formulae summarise some of the the information on these products. The structural types are extensive. For example, (5-phenylalkylphenols have been isolated from several different sources and included are certain bridged biphenyls from Grevillea and Betulaceae species. 

The desirability of having a non-distillation method for larger scale work which would separate the dihydric from the monohydric phenols and permit the recovery of both cardanol and cardol rather than the loss of the latter as a Mannich base product has led to a phase separation method (ref. 190, 191). in this, technical CNSL is distributed between the two immiscible phases of a diol and light petroleum. As a result cardanol enters the upper petroleum phase while cardol and 2-methylcardol are found in the lower diol phase. In this way a highly selective procedure with butane-1,4-diol or pentane-1,4-diol afforded cardanol of greater than 99% purity. 

A variety of poly/dihydric oils are used for the preparation of glyddyl ether-type epoxy resins. These include bisphenols, namely bisphenol-A (BPA), bisphenol-F (BPF), bisphenol-S (BPS) and bisphenol-H (BPH) and so on. Other aromatic diols and polyols such as phenolic resin, MF resins and hyperbranched polyol may also be used in the preparation of vegetable oil-based epoxy resins. Bisphenol-A (2,2-bis(4-hydroxyphenyl)propane) is one of the most widely used aromatic diols for the synthesis of epoxy resin. The resins are commonly used as lacquers for coated metal products such as food cans, bottle tops and water pipes. There are also reports on the use of bisphenol-S (BPS) (bis(4-hydroxyphenyl) sulphone), in the synthesis of epoxy resin. The advantages of resistance to deformation by heat and improvement of thermal stability were observed for such epoxy resins. The presence of sulphone group (BPS-based epoxy resin) in the epoxy resin exhibits better gel time than BPA-based epoxy. Another important diol, namely bis(4-hydroxydiphenyl)methane or bisphenol-F (BPF) is used for the synthesis of low viscosity epoxy resins. BPF generally comprises several isomers such as bis(2-hydroxylphenyl)methane (i.e. ortho-ortho isomer), bis(4-hydroxylphenyl)methane (i.e. para-para isomer) and... 

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