Synthesis of Phenols

Preparation of phenols Heating its aqueous acidic solution converts a diazonium salt to a phenol This IS the most general method for the synthesis of phenols... 

The most widely used industrial synthesis of phenol is based on isopropylbenzene (cumene) as the starting material and is shown m the third entry of Table 24 3 The eco nomically attractive features of this process are its use of cheap reagents (oxygen and sulfuric acid) and the fact that it yields two high volume industrial chemicals phenol and acetone The mechanism of this novel synthesis forms the basis of Problem 24 29 at the end of this chapter... 

The most important synthesis of phenols m the laboratory is from amines by hydrolysis of their corresponding diazonmm salts as described m Section 22 17... 

By far the preponderance of the 3400 kt of current worldwide phenolic resin production is in the form of phenol-formaldehyde (PF) reaction products. Phenol and formaldehyde are currently two of the most available monomers on earth. About 6000 kt of phenol and 10,000 kt of formaldehyde (100% basis) were produced in 1998 [55,56]. The organic raw materials for synthesis of phenol and formaldehyde are cumene (derived from benzene and propylene) and methanol, respectively. These materials are, in turn, obtained from petroleum and natural gas at relatively low cost ([57], pp. 10-26 [58], pp. 1-30). Cost is one of the most important advantages of phenolics in most applications. It is critical to the acceptance of phenolics for wood panel manufacture. With the exception of urea-formaldehyde resins, PF resins are the lowest cost thermosetting resins available. In addition to its synthesis from low cost monomers, phenolic resin costs are often further reduced by extension with fillers such as clays, chalk, rags, wood flours, nutshell flours, grain flours, starches, lignins, tannins, and various other low eost materials. Often these fillers and extenders improve the performance of the phenolic for a particular use while reducing cost. 

Iron impregnated on activated carbon was used as catalyst for the direct synthesis of phenol from benzene. The effect of Sn addition to the catalyst was studied. The prepared catalysts were characterized by BET, SEM and XRD analysis. The catalyst 5.0Fe/AC showed good activity in the conversion of benzene and addition of Sn seemed to improve the selectivity of phenol in the reaction. 

Phenol is the starting material for numerous intermediates and finished products. About 90% of the worldwide production of phenol is by Hock process (cumene oxidation process) and the rest by toluene oxidation process. Both the commercial processes for phenol production are multi step processes and thereby inherently unclean [1]. Therefore, there is need for a cleaner production method for phenol, which is economically and environmentally viable. There is great interest amongst researchers to develop a new method for the synthesis of phenol in a one step process [2]. Activated carbon materials, which have large surface areas, have been used as adsorbents, catalysts and catalyst supports [3,4], Activated carbons also have favorable hydrophobicity/ hydrophilicity, which make them suitable for the benzene hydroxylation. Transition metals have been widely used as catalytically active materials for the oxidation/hydroxylation of various aromatic compounds. 

Phenol-formaldehyde resins using prepolymers such as novolaks and resols are widely used in industrial fields. These resins show excellent toughness and thermal-resistant properties, but the general concern over the toxicity of formaldehyde has resulted in limitations on their preparation and use. Therefore, an alternative process for the synthesis of phenolic polymers avoiding the use of formaldehyde is strongly desired. 

A bi-enzymatic system (glucose oxidase -I- HRP) was also used to catalyze the synthesis of phenolic polymers. The polymerization of phenol, albeit in moderate yield, was accomplished in the presence of glucose avoiding the addition of hydrogen peroxide (Scheme 2 ), which was formed in situ by the oxidation of glucose catalyzed by glucose oxidase. 

Wan, P Hennig, D. Photocondensation of o-hydroxyhenzyl alcohol in an alkaline medium synthesis of phenol-formaldehyde resins. J. Chem. Soc., Chem. Commun. 1987, 939-941. 

Meyers HV, Dilley GJ, Durgin TL, Powers TS, Winssinger NA, Zhu H, Pavia MR. Multiple simultaneous synthesis of phenolic libraries. Mol Diversity 1995 1 13-20. 

The cyclobutenone 70 is transformed to the r/4-vinylketene complex 72 with (t/5-indenyl)Co(PPh3)2 71. The vinylketene complex 72 undergoes cyclization with alkynes to produce the corresponding phenols 73. FeCl3 oxidation of the (2-phenylvinyl)ketene complex, however, leads to the naphthol 74. A catalytic synthesis of phenols via the vinylketene intermediates 72 is achieved by the use of Ni(COD)2 as a catalyst [36]. (Scheme 26)... 

Reihmann, M. and Ritter, H. Synthesis of Phenol Polymers Using Peroxidases. Vol. 194, pp. 1-49. 

This chemistry was developed with the specific intention of application to the synthesis of phenols. There had only been one previous example of the addition of alkynes to 774-vinylketene complexes yielding phenols,22 despite a cornucopia of other organic fragments having been isolated from such reactions (see Sections II, V, and VI). The best results were obtained on reaction of the 3-phenylvinylketene complex 114.a with several alkynes. 

Since zeolite catalysts are successfully introduced in the refining and petrochemical industries, it is not surprising that most of the recent advances concern incremental improvements of existing processes with the development of new generations of catalysts (e.g., dewaxing, ethylbenzene and cumene synthesis). The number of newer applications is much more limited, for example, direct synthesis of phenol from benzene and aromatization of short-chain alkanes, etc. However, both the improvement and development of processes contribute significantly to environmental advances. 

T1 resin traceless linker [131-134], synthesis of phenols [135], biaryls, alkyl arenes [136, 137], azides [138], aromatic hydrazines, halides [cf. 128, 129, 139], ester, azo compounds, cinno-lines [140], benzotriazoles [141]... 

It is used in the manufacture of polyvinylpyrrolidone (PVP), in the manufacture of copolymers with, for example, aciv lic acid, acrylates, vinyl acetate and acrylonitrile and in the synthesis of phenolic resins. About 10-15% of the monomer is used in the pharmaceutical industry for the production of PVP-iodine complex used as a disinfectant. It is also used as a reactive solvent of ultraviolet-curable resins for the production of printing inks and paints as paper and textile auxiliaries, and as an additive in the cosmetics industry (Harreus, 1993). 

The related manufacture of cumene (isopropylbenzene) through the alkylation of benzene with propylene is a further industrially important process, since cumene is used in the synthesis of phenol and acetone. Alkylation with propylene occurs more readily (at lower temperature) with catalysts (but also with hydrogen fluoride and acidic resins) similar to those used with ethylene, as well as with weaker acids, such as supported phosphoric acid (see further discussion in Section 5.5.3). 

The most widely used industrial synthesis of phenol is based on isopropylbenzene can you recall howto pre-... 

This is Kolbe s synthesis of phenolic acids. It is capable of very wide application. In all cases the carboxyl group primarily seeks the or o-position if that is occupied, some condensation in the para-position occurs. The following are some examples. 

Alkylation of /j-cresol by isobutylene is an important reaction in the synthesis of phenolic antioxidants. The activity of H3PW 2O40 for this reaction is greater by four orders of magnitude than that of H2S04 (160). Alkylation of p-(tert-butyl)phenol (TBP) with cyclohexene, 1-hexene, styrene, or benzyl chloride proceeds in the presence of H3PW 204o at 3373-423 K (204). 

If the products contain an enolizable hydrogen, overoxidation is a concern. When cyclopentanones are involved, the cyclic products are often more rapidly oxidized than the starting materials. However, further oxidation of the cyclic products is not necessarily undesirable. For example, Snider has developed a simple synthesis of phenols in which a manganese(III)-mediated 6-endo radical cyclization is followed by oxidative aromatization.154 An example of this process is provided in Scheme 34. Snider has also shown that the overoxidation can be blocked with a chlorine atom, as shown by the second example in Scheme 34.153... 

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