Phenols and Their Uses

Historically, the outbreak World War I provided a stimulus for the industrial preparation of large amounts of synthetic phenol, which was needed as a raw material to manufacture the explosive, picric acid (2,4,6-trinitrophenol). Today, approximately 8 million metric tons of phenol is manufactured worldwide each year for use in such products as Bakelite resin and adhesives for binding plywood. 

Phenol was manufactured for many years by the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.8). Now, however, an alternative synthesis from isopropylbenzene, commonly called cumene, is used. Cumene reacts with air at high temperature by benzylic oxidation through a radical mechanism to form cumene hydroperoxide, which is converted into phenol and acetone by treatment with acid. This is a particularly efficient process because two valuable chemicals are prepared at the same time. 

I Protonation of the hydroperoxy group on the terminal oxygen atom gives an oxonium ion... 

I Nucleophilic addition of water to the carbocation yields another oxonium ion... 

which rearranges by a proton shift from one oxygen to another. 

Phenol was manufactured for many years by the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.S). Now, however, an alternative synthesis from isopropylbenzene, commonly called 

In addition lo its use in making resins and adhesives, phenol is also the starting material for the synthesis of chlorinated phenols and the food preservatives BHT (butylated hvdroxytoiuene) and BHA (butylated bydroxyanisole). Penta-chlorophenol, a widely used wood preservative, is prepared by reaction of phenol with excess CI2- The herbicide 2,4-D (2,4-dichlorophenoxyacetjc acid) is prepared from 2,4-dichlorophenol, and the hospital antiseptic agent hexa-chlorophene is prepared from 2,4,5-trichlorophenol. 

The food preservative BHT is prepared by Friedel-Crafts alkylation of p-methylphenol (p-cresol) wnth 2-methyIpropene in the presence of acid BHA is prepared similarly by alkylation of p-methoxyphenok 

Problem 17.17 Show the mechanism of the reaction of p-methylpheno) with 2-methylpropene and H3P04 catalyst to yield the food additive BHT. 

Mechanism of the formation of phenol by acid-catalyzed rearrangement of cumene hydroperoxide. 

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Triaryl phosphates are produced by reaction of phosphoms oxychloride with phenoHc compounds at 100—200°C with magnesium or aluminum chloride catalyst. Past use of cresols and xylenols from coal tar or petroleum is replaced for lower toxicity and cost by synthetic phenoHcs, primarily isopropyl phenol, /-butyl phenol, and phenol itself A range of viscosities is achieved by selection and proportioning of the phenols and their isomers used for the starting material. 

Closely related to the use of rhodium catalysts for the hydrogenation of phenols is their use in the reduction of anilines. The procedure gives details for the preparation of the catalyst and its use to carry out the low-pressure reduction of /j-aminobenzoic acid. Then, as in the preceding experiment, advantage is taken of the formation of a cyclic product to carry out the separation of a mixture of cis and trans cyclohexyl isomers. 

Formylation with Zn(CN)2 and HCI is called the Gatterman reaction It can be applied to alkylbenzenes, phenols and their ethers, and many heterocyclic compounds. However, it cannot be applied to aromatic amines. In the original version of this reaction, the substrate was treated with HCN, HCI, and ZnCl2, but the use of Zn(CN)2 and HCI (HCN and ZnCF are generated in situ) makes the reaction more... 

A number of handbooks and monographs are available with detailed descriptions of a variety of plant products and their use (Shahidi and Naczk, 1995). From a more practical point of view, an interlaboratory comparison between six university and industry laboratories of 17 extracts of spices, teas, coffees, and grape skin and of tomato peel slurry established within the framework of an EU sponsored programme, would be of interest (Schwarz et al, 2001). In this collaboration, detailed chemical analysis of the content of different phenolic compounds is compared with six antioxidant assays for the 17 extracts including different extraction procedures. 

The United States production of amino plastics was more than 3 billion pounds in 2001. The urea-formadehyde polymers account for slightly more than 85% of the total. The amino plastics are similar in properties to the phenolics but are clearer and colorless. They are also harder but have somewhat lower impact strength and resistance to heat and moisture. The melamine resins are better than the ureas in hardness and resistance to heat and moisture. The melamine and urea resins are rated for continuous use at temperatures of 130-150°C and 100°C, respectively. The general applications of the amino and phenolic plastics are the same but there are uses where the amino plastics are superior. The melamine resins find an important niche due to their combination of clarity and lack of color compared to the phenolics and their superior hardness and heat and moisture resistance compared to... 

Saponins are generally extracted from plants through an alcoholic extraction of the defatted vegetable material. Due to the possible contemporary presence of acidic components (phenols and their acids, flavonoids, etc.) care should be taken about the pH of the alcoholic solution, which, if too low, can produce undesidered chemical modifications. Acidic methanol can hydrolize glycosidic bonds or produce transesterification. A subsequent useful step is the partition of the total dried alcoholic extract between n-butanol and water. This operation is important to eliminate mono- and disaccharides which complicate further separations. 

Obtain energies for each ion and for their corresponding precursors (benzoic acid,phenol and cyclohexanol). Use this information to calculate the energy for each of the above deprotonation reactions. (The energy of proton is given at left.) Is the trend consistent with the experimental pKa data (see table at left) Does deprotonation energy parallel charge delocalization in these systems Explain how electron delocalization affects the reactivity of these acids. 

This method is particularly useful for the synthesis of phenoxides and tends to work well due to both the increased acidity of phenols and their lower volatility relative to alcohols. Hence phenoxides of a large number of elements have been prepared by this route including main group,85 d-block,86 lanthanides87 and actinides88 (equations 18, 19 and 20). 

Francis, A.J., Morgan, E.D., and Poole, C.F., Flophemesyl derivatives of alcohols, phenols, amines and carboxylic acids and their use in gas chromatography with electron-capture detection, J. Chromatogr., 161, 111, 1978. 

A history of ether and etherification is a welcome, and now rare, focus on an individual compound.72 It covers work by Berzelius, Gerhardt, Hennell, Kolbe, Liebig, and of course Williamson. Acetoacetic ester has received detailed historical notice in a biography,73 as have salicylic acid and the salicylates.74 Apart from natural products, few heterocyclic substances have been recently the subject of historical enquiry. An impressive exception is that of pyrrole, a simple molecule explored by Dippel, Reichenbach, Runge and others, and manufactured by Du Pont.75 There is also an account of the structural problems posed by piperidine.76 Accounts have been given of the discovery of aniline from crystallin (a product of the thermal decomposition of indigo),77 of the history of phenol over the last two centuries,78 and of organic nitrates and their uses in medicine.79... 

New terpolymers of vinyl acetate with ethylene and carbon monoxide have been prepared and their uses as additives to improve the curing and flexibility of coating resins, eg, nitrocellulose, asphalt, phenolics, and polystyrene, have been described (130—132). Vinyl acetate and vinylidene cyanide form highly alternating copolymers. 

Rearrangement of phenols to dienones occurs readily in superacids. Some simple bicyclic phenols and their ethers have been investigated as model compounds by use of HF-SbFs [73]. This method is also applicable to natural products [74]. For example, treatment of estrone derivatives in HF-SbFs, then aqueous bicarbonate work-up led to estra-4,9-diene-3,17-dione (Eq. 30). The opposite rearrangement, i.e. that of dienones to phenols, can also be achieved in an HF-SbFs medium (Eq. 31) [75]. 

Bromination of para-alkylated or 2,6-dialkylated phenols and their ethers with Br2 in HF-SbFs leads to the formation of mera-brominated products (Eq. 47) [106]. Sodium or potassium bromide can also be used in place of Br2 in this reaction [107]. 

Flow Injection Analysis of Phenols and Conjugates. In order to determine the mode of ionization giving maximum sensitivity, FIA was used to obtain mass spectra of the individual standards of the phenols and their conjugates in both acetonitrile and acetonitrile-pH 4.5 ammonium formate (2 3, v/v) using El, methane PCI and NCI, and isobutane PCI and NCI. Operating conditions were flow rate, 0.4 mL/min desolvation chamber temperature,... 

Negative ion thermospray (TSP) tandem mass spectrometry (MS/MS) was used to determine phenols and their corresponding glucuronide and sulfate conjugates. 

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