phuric acid. They may be separated by means of their potassic salts, the para compound being the more insoluble.

Metatoluene sulphonic acid is obtained by reduction of orthochlortoluene metasulphonic acid by means of sodium amalgam.

Homologues of Toluene.

1018. Ethyl-benzene, CH5.C2H5, is obtained by the action of sodium on a mixture of brom-benzene and ethylic bromide, or by heating ethylic chloride and benzene in the presence of aluminic chloride.

It is a colourless liquid, of b.p. 134° and sp. gr. ·8664. On oxidation benzoic acid is produced. Chlorine acts on boiling ethyl benzene, forming phenethyl chloride, CH5.CH.CH2Cl. At the ordinary temperature the chlorine enters the aromatic nucleus. With bromine, however, the reverse reaction appears to take place to a great extent, B-phenethyl bromide :

being formed.

CH.CHBr.CH 3,

Several nitro derivatives have been formed (§ 1013).

Paranitro-ethyl benzene, b.p. 245°-246°; ortho, b.p. 227°–228°. They yield corresponding amido-ethyl benzenes, CH1(NH2).C2H5, on reduction.

With concentrated sulphuric acid ethyl benzene gives two sulphonic acids, CH,(SO2OH).(CH). The one formed in largest quantity on fusion with potash gives an ethyl phenol, CH(OH)CH, which melts at about 47° and boils at 210°. It is not known for certain if it be the para or ortho product.

Phlorol, which is obtained by the distillation of phloretic acid with lime, appears to be an isomer of ethyl phenol, but its constitution is as yet uncertain. It is a liquid boiling at 220° which does not solidify at -18°.

Coal and beech-wood tar also contain phenols of the formula CH100, which, however, are not well known. They give, on distillation with oxidising agents, a quinone, phlorone, CH ̧O2, which sublimes in light yellow needles and is converted by nascent hydrogen into hydrophlorone, C,H,(OH)2, forming easily soluble colourless crystals.

1019. Propyl-benzene, CH5.CH2.CH2.CH3, has been obtained synthetically by the action of sodium on a mixture of a-iodo-propane and monobrom-benzene. It boils at 157°. Isopropyl benzene, similarly obtained, and also prepared from cumic acid by distillation with lime:

[C&H (C3H7).CO.O],Ca + Ca(OH)2 =2CaCO3

+2C6H5.CH.(CH3)2,

boils at 151°, and hence is termed cumene. acid on oxidation.

They both yield benzoic

Isobutyl benzene, CH5.CH2.CH(CH3)2, is a colourless oil, boiling at 160°.

Isoamyl benzene, C6H5.CH2.CH2.CH(CH3)2, boils at 193°. Isohexyl benzene, CH5.CH2.CH2.CH2.CH(CH3)2, prepared by the action of sodium on benzylic chloride and isoamylic bromide, boils

at 214°.

1020. Dialkyl benzenes may be obtained from the monobrom substitution products of the monalkyl benzenes in a similar manner to the production of the latter from brom-benzene itself:

CH,Br(CnH2n+1)+ BrCnH2n+1 + Na2 = 2NaBr

+C.HọC Hr+
.CnH2n+1

n'

The dibrom-benzenes also yield the same bodies to some extent: C6H4Bг2+2BrCnH2n+1 = 2Na2 = 4NaBr + CH1(CnH2n+1)2° The dimethyl compounds, when submitted to the action of dilute nitric acid, give methyl-benzoic acids; e.g.

.CH3

CH,(CH3)2 + 30 OH2+ CHACO.OH
= 2

Chromic acid, however, oxidises the para compounds to terephthalic acid, the meta compounds to isophthalic acid :

C6H4(CH3)2 + 302 = 20H2 + C6H1(CO.OH)2,

the ortho compounds being completely destroyed.

When acted upon at their boiling points by the halogens, substitution products are formed, having the halogen in the alkyl group : CH1(CH3)2 + Cl2 = C6H4(CH3).CH2Cl + HCl.

When kept cold, however, or in the presence of iodine, substitution takes place at the benzene nucleus :

CH,(CH3)2 + Br2 = C6H3Br(CH3)2 + HBr.

Fuming nitric acid forms nitro substitution products, in which the substitution has taken place on the benzene group, which may be reduced by nascent hydrogen to azo and amido products, and these in their turn converted by means of nitrous acid into diazo compounds.

Dimethyl Benzenes, Xylenes, C8H10 = C6H4(CH3)2.

1021. Light coal-tar oil gives, on distillation, a fraction boiling between 136° and 139°, consisting of a mixture of meta- and paraxylene, which cannot be separated by fractional distillation.

=

Orthoxylene 1:2 is prepared synthetically by the action of sodium on a mixture of orthobrom-toluene and methylic iodide diluted with ether. It is a colourless oil, boiling between 140° and 141°. With dilute nitric acid it is oxidised to orthotoluic acid. On heating for some time with a mixture of fuming nitric and sulphuric acids, trinitro-orthodimethyl benzenes are produced. Paraxylic acid also gives orthoxylene on distillation with lime or baryta.

Metaxylene, (1:3), is obtained pure by the distillation of xylic or mesitylenic acids with lime. It boils at 137°, is not attacked by dilute nitric acid, but is converted by chromic acid into isophthalic acid.

Paraxylene, (1:4), prepared by the action of sodium on crystalline parabrom-toluene mixed with methylic iodide and benzene, or from

Nitro-motazylene melta at 25 and bella at 2371-2197.

2167

22

Amilo meringlene, C ̧H2(NH ̧•CH, is also liquid and beûs at Dinitro metarylene meita at 931 and forms colourless flattened Xylofins, CM/NH2//CH22 Three liquid isomers are known. The metaxylidine boils at 2165 Paraxylidine boils at 2207-221.

Dimethyl Phenola, CH (CH2),OH, Xylenols.—Two isomers are known, and may be obtained from the coal-tar xylol mixture of oils by conversion into the sulphonic acids and fusion of these with potassic hydrate. Coal tar xylenol consists principaily of the meta compound, and yields metadimethyl oxybenzene, a soluble solid, melting at 75° and boiling at 216. When acted on by bromine, a dibromide, melting at 1, is produced. The potassic salt of mesitylene sulphonic acid, when fused with potash, also gives metaxylenol. The other isomeric xylenol is liquid and boils between 211°-212°.

It is also very likely that the phenols of the formula C.H100, obtainable from heavy coal tar oils (§ 1018), are xylenols, in which ee phlorone may be a dimethyl quinone, CH(CH3)2O2.

1022. Ethyl methyl benzenes, CH12 = C6H1.C2H2 Meta-ethyl

methyl benzene is obtained from metabrom-toluene and ethylic iodide by the netion of sodium It boils between 158° and 159°.

Para ethyl methyl benzene boils at 161°-162°, and does not solidify at

18".

1023. Dialkyl benzenes, CH14. 1. Paradiethyl benzene :

CH(CH)2,

from parabrom ethyl benzene, ethylic bromide, and sodium, is a liquid boiling between 178° and 179°. It gives ethyl-benzoic acid on

oxidation.

.CH3

2. Cymene, parapropyl-methyl benzene, CHACH, (1:4), is contained in various ethereal oils-e.g. Roman cumin oil, from the seeds of Cuminum Cyminum, in oil of nutmeg, oil of Cicuta virosa, or water hemlock, &c. It may be obtained from some terpenes, C10H16, by the long-continued action of iodine or by heating camphor with phosphoric anhydride or pentasulphide, or with zinc chloride:

It may also be obtained synthetically from primary propylic iodide and parabrom-toluene by the action of sodium.

Cymene is a colourless oil, boiling at 175° with an odour faintly recalling that of lemons. It gives paratoluic acid, CH,(CH3).CO.OH, on oxidation with dilute nitric acid. Fuming nitric acid converts it into a mixture of nitro-cymenes, of which one is liquid and volatile in a current of steam and another solid (m.p. 125°) and non-volatile. With concentrated sulphuric acid a cymene sulphonic acid is produced, which gives cymophenol, CH(OH)CH, .CH3 on fusion with

alkalies. It is a thick oil, boiling at 232°. The same body is also produced when camphor is heated with iodine:

C10H160+ I2 = 2HI + C10H10.

Thymol, CH3(CH3)(C3H,a).OH, is a propyl-methyl-phenol isomeric with carvacrol. It is obtained from oil of thyme by shaking with aqueous alkalies. It forms large crystals, melting at 44° and boiling at 230°. Nearly insoluble in water, but dissolving easily in alcohol and ether.

On heating with phosphoric anhydride metacresol phosphate and propylene are formed. With phosphoric sulphide thio-thymol, CH2SH C¡«, b.p. 233°-235°, is produced. .CH a,

On oxidation with manganic oxide and sulphuric acid, thymoquinone, CH2O, CH3

6 2 2.C3H7 a,

results.

It forms yellow needles of a pungent odour, melting at 45.5°.
.CH,

Sulphites reduce it to thymhydroquinone, C¿H2(OH)2 C2H‚ ̈

Carvacrol, the isomer of thymol, is obtained by the action of phosphoric acid on carvol, a substance contained in Roman oil of caraway; by heating camphor with one-third of its weight of iodine; and from paramethyl-propyl-benzene sulphonic acid by fusion with potash. It is probable that in thymol the hydroxyl occupies the meta position with regard to the methyl, whilst in carvacrol it occupies the ortho position :