Chemistry · Ch 13 — Hydrocarbons
Sources of Aromatic Compounds
Sources of Aromatic Compounds
Benzene and other aromatic compounds are obtained from coal tar and petroleum, and can also be synthesised in the laboratory from simple aliphatic starting materials, as deta …
Industrial Preparation of Benzene from Coal Tar
Coal tar, a viscous liquid obtained by pyrolysing coal, is fractionally distilled to separate its many volatile aromatic components by boiling-point range; benzene, toluene and xylene distil off together in the lowest-boiling ('crude li …
| Name of the Fraction | Temperature Range | Name of the Components |
|---|---|---|
| 1. Crude light oil | 350-443 K | Benzene, Toluene, Xylenes |
| 2. Middle oil | 443-503 K | Phenol, Naphthalene |
| 3. Heavy oil | 503-543 K | Naphthalene, Cresol |
Other Methods of Preparing Benzene and Toluene
FROM ACETYLENE: passing acetylene through a red-hot iron tube trimerises it directly to benzene (the same cyclic-polymerisation reaction already met under alkynes), 3 CHCH --873K--> C6H6. LABORATORY METHODS: (a) Decarboxylation of an aromatic acid -- heating sodium benzoate with soda lime distils over benzene vapour, C6H5COONa + NaOH --CaO, heat--> C6H6 + Na2CO3. (b) Preparation from phenol -- passing phenol vapour over zinc dust reduces it to benzene, C6H5OH + Zn --> C6H6 + ZnO. (c) Wurtz-Fittig reaction -- treating a solution of bromobenzene and iodomethane in dry ether with metallic sodium gives toluene, C6H5Br + ICH3 + 2Na --dry ether--> C6H5CH3 + NaBr + NaI. (d) Friedel-Crafts reaction -- trea …
Worked out. Asks how benzene can be prepared using a Grignard reagent -- by hydrolysing phenylmagnesium bromide (C6H5MgBr, itself made from bromobenzene + Mg in dry ether) with water/a proton source, giving benzene + Mg(OH)Br, exactly analogous to the alkane-from-Grignard-reagent method met earlier in the chapter. …