GROUP MEMBERS
1.ODHIAMBO BRIAN ODHIAMBO EN251-0427-2014
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INTRODUCTION
Phenol is the monohydroxyl benzene(Isopropylbenzene) C6H5OH having a characteristic odour and when very dilute, a sweetish taste.
Coal tar was the only source of phenol almost until World War I. Then came various synthetic routes. The modern phenol industry is based on the pioneering work in Germany by Dr. Heinrich Hook and SonLang in 1944 on the oxidation of cumene to cumene hydroperoxide which under the influence of an acidic catalyst would decompose into phenol and acetone.
Phenol is toxic and corrosive. In case of accidential contact, the area exposed should be rapidly and throughly washed with a mild alkaline solution.
The most significant products from phenol are phenolic resins, Bisphenol A, Caprolactam and salicylic acid.
The industrially important methods of manufacture of phenol are as follows:
Cumene Oxidation process, (ii) Toluene Benzoic Acid process. (iii) Sulphonation process; (iv) Chlorobenzene process. (v) Rasching Hooker process.
Today cumene oxidation process is the only commercially significant route for the production of phenol. This process also gives a very important co-product acetone.
In this assignment we describe into details the cumene oxidation (Hock )process of manufacture of phenols.
This process uses two relatively cheap raw materials, benzene and propylene, into two more valuable ones phenol and acetone. Other reactants required are oxygen from air and small amounts of a radical initiator ( substances that can produce radical species under mild conditions and promote radical reactions) In order for this process to be economical, there must also be demand for the acetone by-product as well as the phenol.
(GENERAL EQUATION FOR CUMENE PROCESS)o
THE CUMENE OXIDATION PROCESS
The manufacture of phenol process consists of the following stages :
1.Cumene Synthesis.
2.Oxidation of cumene
3.Hydrolsis of cumenehydroperoxide into phenol and acetone.
4. Purification of phenol
STAGE 1: CUMENE SYNTHESIS.
Benzene and propylene are compressed together to a pressure of 30 atmospheres 250 °C in presence of catalytic lewis acid. phosphoric acid is favoured over aluminium halides.Cumene is formed in the gas-phase .
STAGE2: CUMENE OXIDATION .
Cumene is oxidized in air which removes the tertiary Benzilic hydrogen from cumene and hence forms a cumene radical.
This cumene radical then bonds with an oxygen molecule to give cumene hydroperoxide radical, which in turn forms cumene hydroperoxide (C6H5C(CH3)2-O-O-H) by abstracting benzylic hydrogen from another cumene molecule.
This reaction is carried out at temperatures of 90 - 130ºC and pressures of 1-10 atmospheres. Careful control of acidity levels, temperature and pressure are mandatory as at higher temperatures, the hydroperoxide is unstable and can decompose violently.
The high pressure is keep the unstable cumene hydroperoxide in a liquid state.
To help reduce the risk of this happening, only 25% of the cumene is allowed to react at any one time in order to keep the concentration of the hydroperoxide within safe limits. Un-reacted cumene has to be separated out and recycled, adding to the costs.
This step also produces major impurities of the process.
3.HYDROLYSIS OF CUMENE HYDROPEROXIDE(CLEAVAGE REACTION)
The hydroperoxide is mixed with dilute sulphuric acid at 60 - 70ºC, to produce both phenol and propanone (acetone) as products. The decomposition of cumene hydroperoxide to phenol and acetone is often described as a cleavage reaction.(hydrolysis in an acidic medium)
Two useful products are therefore obtained, phenol and propanone. However, this means the production of phenol is in part dependent on the demand for propanone, which is rising at a lower rate than phenol, and so in the future propanone may become a waste product.
In the first step, the terminal hydroperoxyl oxygen atom is protonated. This is followed by a step in which the phenyl group migrates from the benzyl carbon to the adjacent oxygen and a water molecule is lost, producing stabilized tertiary carbocation.
the resulting carbocation Is then attacked by water, a proton is then transferred from the hydroxyl oxygen to the ether oxygen, and finally the ion falls apart into phenol and acetone.
4.PURIFICATION OF PHENOL
The process involves contacting phenol in the liquid phase with a basic reagent at a temperature in the range of about 20 C. to about 250 C. for at least about 0.25 hour, fractionally steam distilling the phenol and finally subjecting the treated phenol to fractional distillation to recover a purified phenol.
INDUSTRIAL USES OF PHENOL
Phenol-methanal (formaldehyde) resins are the basis of the oldest plastics, and are still used to make low cost thermosetting plastics such as melamine and bakelite, used in electrical equipment. These resins are also used extensively as bonding agents in manufacturing wood products such as plywood and MDF.
Phenyl amine(an intermediate of phenol ) is used as an antioxidant in rubber manufacture, and as an intermediate in herbicides, dyes and pigments, and pharmaceuticalsIt is used to make isocyanates for the production of polyurethanes, with a wide range of uses from paints and adhesives to expanded foam cushions(for vehicles seat).
Concentrated phenol liquids are commonly used in the surgical treatment of in grown toe-nails to prevent a section of the toenail from growing back. This process is called phenolization.
4. Bisephonol –A an intermediate of phenol is Used to produce epoxy resins for paints coatings and mouldings, and in polycarbonate plastics, familiar in CDs and domestic electrical appliances.
5.Alkyl phenols are used in the manufacture of detergents and emulsifiers, and also in insecticide and plastics production.
