Replacement by phenol

Monovalent copper salts were initially found to be better catalyst precursors than divalent copper salts. The latter needed the addition of base. In the presence of dioxygen the copper(I) salts are oxidised to copper(II) hydroxides forming hydroxide bridged dimers. The hydroxides can be replaced by phenolates, thus producing the key-intermediate [23] (Figure 15.16). From this equilibrium we understand that water concentration should be kept low in order to have a maximum amount of phenoxides coordinated to the copper dimers. 

Application development for phenolics has been spurred by weight and cost savings inherent in metal replacement and parts consolidation. Thermoplastics have been replaced by phenolics where creep resistance and thermal stability are required in downsized parts or applications in hostile environments. 

Because of their increased acidity, it is possible for phenols to effect total substitution of halide ligands in cases where alcohols cause only partial substitution. Hence, although WC16 reacts with ethanol to give the Wv complex [WCl3(OEt)2]2,35 phenol in benzene gives W(OPh)6 in excellent yields.4,36 Similarly, the phenoxides of Ti,37 Nb and Ta38 have been obtained. In cases where only partial replacement by phenol occurs, the use of substituents that increase the phenolic acidity can sometimes aid the reaction, for example as shown in equation (7).39,4(1... 

The original acid-clay developers have been largely replaced by phenolic compounds, such as para-substituted phenolic novolaks. The alkyl group on the phenolic ring is typically butyl, octyl, nonyl, or phenyl. The acidity is higher than that of a typical unsubstituted novolak because of the high concentration of 2,2 -methylene bridges. 

The mostly commonly used approach with PCI3 (Scheme 2.85, Route I Scheme 2.87) proceeds best in the presence of a base (e.g., ammonia, trialky-lamines, pyridine). If different alcohols are to be linked, a two-step approach is recommended to avoid the formation of hgand mixtures. In large-scale reactions, no solvent is required. For a smaller setup, the reaction is conducted commonly in nonpolar solvents such as THF (tetrahydrofuran) or toluene [67]. The reaction with aromatic alcohols proceeds in three steps, in which three chlorine atoms [68] are successively replaced by phenols. 

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

Picric acid, the 2 4 6-trinitro derivative of phenol, cannot be prepared in good yield by the action of nitric acid upon phenol since much of the latter is destroyed by oxidation and resinous products are also formed. It is more convenient to heat the phenol with concentrated sulphuric acid whereby a mixture of o- and p-phenolsulphonic acids is obtained upon treatment of the mixture with concentrated nitric acid, nitration occurs at the two positicsis mela to the —SOjH group in each compound, and finally, since sulphonation is reversible, the acid groups are replaced by a third iiitro group yielding picric acid in both cases ... 

If formaldehyde is replaced by furfural, the furfural - phenol polymer (U.S.A. Durite) results. The above polymers are largely used for moulding purposes. 

The synthesis of chlorarul [118-75-2] (20) has been improved. The old processes starting from phenol or 2,4,6-trichlorophenol have been replaced by new ones involving hydroquinone chlorination. These processes allow the preparation of chlorarul of higher purity, avoiding traces of pentachlorophenol. Different types of chlorination conditions have been disclosed. The reaction can be performed according to the following stoichiometry, operating with chlorine in aqueous acetic acid (86,87), biphasic medium (88), or in the presence of surfactants (89). 

Wood Bonding. This appHcation requires large volumes of phenoHc resins (5—25% by weight) for plywood, particle board, waferboard, and fiberboard. Initially, phenoHc resins were used mainly for exterior appHcations, whereas urea—formaldehyde (UF) was used for interiors. However, the concern over formaldehyde emission has caused the replacement of UF by phenol-formaldehyde adhesives. 

One-part urethane sealants (Table 3) are more compHcated to formulate on account of an undesirable side reaction between the prepolymer s isocyanate end and water vapor which generates carbon dioxide. If this occurs, the sealant may develop voids or bubbles. One way to avoid this reaction is to block the isocyanate end with phenol and use a diketamine to initiate cure. Once exposed to moisture, the diketamine forms a diamine and a ketone. The diamine reacts with the isocyanate end on the prepolymer, creating a cross-link (10). Other blocking agents, such as ethyl malonate, are also used (11). Catalysts commonly used in urethane formulations are tin carboxylates and bismuth salts. Mercury salt catalysts were popular in early formulations, but have been replaced by tin and bismuth compounds. 

Titanium Silicates. A number of titanium siUcate minerals are known (160) examples are Hsted in Table 19. In most cases, it is convenient to classify these on the basis of the connectivity of the SiO building blocks, eg, isolated tetrahedra, chains, and rings, that are typical of siUcates in general. In some cases, the SiO units may be replaced, even if only to a limited extent by TiO. For example, up to 6% of the SiO in the garnet schorlomite can be replaced by TiO. In general, replacement of SiO by TiO bull ding blocks increases the refractive indices of these minerals. Ti has also replaced Si in the framework of various zeofltes. In addition, the catalytic activity of both titanium-substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) has received attention (161), eg, the selective oxidation of phenol, with hydrogen peroxide, to hydroquinone and catechol over TS-1 has been operated at the 10,000 t/yr scale in Italy (162). 

Here X and Y are immobilizing groups. Fuji instant color films are based on a similar dye-release mechanism using the o-sulfonamidophenol dye-release compounds shown in Figure 8 (35). Similarly, immobilej -su1fonamidoani1ines, where Y is H and the phenol group is replaced by an NHR moiety, may be used as dye releasers. 

With the advent of these compounds in the 1960s, the hitherto more conventional insulating materials, such as phenol formaldehyde (popularly known as Bakelite) and wood (veneered impregnated) have been almost replaced by them. These compounds offer better electromechanical properties than conventional materials. Below we describe the basic mix and properties of these two basic compounds, for a brief reference. 

Whilst remaining speciality materials, several copolymers have been marketed ver the years in order to enhance certain specific properties whilst retaining the eneral characteristics of polycarbonates. There are also a number of homo-olymers in which the bis-phenol A has been replaced by another bis-phenol ompound. The most important of these are summarised below. 

To enhance the resistance to heat softening his-phenol A is substituted by a stiffer molecule. Conventional bis-phenol A polycarbonates have lower heat distortion temperatures (deflection temperatures under load) than some of the somewhat newer aromatic thermoplastics described in the next chapter, such as the polysulphones. In 1979 a polycarbonate in which the bis-phenol A was replaced by tetramethylbis-phenol A was test marketed. This material had a Vicat softening point of 196 C, excellent resistance to hydrolysis, excellent resistance to tracking and a low density of about l.lg/cm-. Such improvements were obtained at the expense of impact strength and resistance to stress cracking. 

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

Today the phenol-formaldehyde moulding compositions do not have the eminent position they held until about 1950. In some, important applications they have been replaced by other materials, thermosetting and thermoplastic, whilst they have in the past two decades found use in few new outlets. However, the general increase in standards of living for much of this period has increased the sales of many products which use phenolics and consequently the overall use of phenol-formaldehyde moulding powders has been well maintained. 

Dichloroquinone-4-chloroimide, which can be replaced by 2,6-dibromoqui-none-4-chloroimide (qv.) reacts preferentially with phenols and anilines which are not substituted in the />-position [2]. 

Corypalline, CnHijOjN (Corydalis spp. Nos. 9, 22 list, p. 170). This phenolic base, m.p. 168°, picrate, m.p. 178°, contains one methoxyl group and on methylation yields 2-methyl-6 7-dimethoxytetrahydrof5oquinoline, Ci2Hi,02N, m.p. 82°, and on ethylation, 2-methyl-6-methoxy-7-ethoxy-tetrahydrofsoquinoline, m.p. 65°, whence the free hydroxyl appears to be at C and this has been confirmed by the synthesis of corypalline by a method analogous with that used by Spath, Orekhov and Kuffner. Corypalline is therefore hydrohydrastinine (XII) with the methylenedioxy group replaced by MeO at C and. OH at C (Manske). ... 

Mix I gram of phenol with i c.c. of dimethyl sulphate and add 4 c.c. of a lo per cent, solution of caustic soda. Warm and shake. The odour of phenol is replaced by that of anisole, which can be extracted from the licjuid by ether (Ullmann s reaction). See Appendix. p. 294. 

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