CH3

tonic acids, C=O, and many similar complications, which with some

CO.OH

less known categories of transformation and substitution-derivatives of the paraffins will be mentioned at their respective places.

146. The series of paraffins contains members with nuclei of from one to at least thirty atoms of carbon, and their isomers. Those poorest in carbon are gases; by increasing carbon contents liquids and solids follow, whose boiling and melting points increase, as a rule, with the increase in molecular weight. They are nearly or quite insoluble in water, burn easily when heated in an oxygen-containing atmosphere, and are converted into substitution-derivatives by the action of the halogens-especially chlorine-when exposed to light or heat: CnH2n+2 + Cl2 = HCl + С2H2n+1 Cl

2

CnH2n+2+2Cl2 = 2HCl + CnH2nCl2

CnH2n+2+3Cl2 = 3HCl + C2H2n-1 Cl3

&c.

Many paraffins are also attacked by strong nitric acid, water being eliminated, and a product formed which contains the nitric acid radical NO, (nitryl) in place of hydrogen. Such bodies are termed nitro-paraffins. The paraffins are very indifferent to most reagents.

Occurrence and Formation of the Paraffins.

147. Many hydrocarbons of the marsh-gas series occur readyformed in nature; they are formed mostly by the decomposition of dead putrefying or decaying organisms, and are therefore very frequently found with coal. The liquid and solid paraffins form the chief proportion of mineral oil or petroleum, from which a large number of members of the series have been isolated by fractional distillation.

Paraffins are also formed in the dry distillation of many organic bodies, though, with the exception of the gaseous members, only in small quantity and varying proportion. The latter depends on the temperature employed and the duration of the heating, and cannot at present be deduced into a rule approaching certainty. On the other hand, a series of reactions are known which serve for the preparation of individual members of the series.

148. Synthetical Methods of Preparing Paraffins.-No paraffin has been prepared as yet by the direct action of carbon upon hydrogen; marsh gas, however, has been obtained by means of very simple mineral compounds (see later). The above-mentioned methods of the synthesis of paraffins are from already existing organic bodies, and fall into two groups, accordingly as the transformation takes place on already existing carbon nuclei, without increase thereof, or by the synthetical formation of the nucleus by combination of simpler carbon nuclei, this latter being known as nucleus-synthesis. Of both methods the following may be mentioned as the most important.

149. Methods without Increase of Nucleus.-These consist without exception in joining the maximum number of hydrogen atoms to the nucleus chosen.

For such methods the zinc compounds of the monovalent alcohol radicals are most particularly available. They react with water, according to the equation

CH2n+1
Zn C2H2n+1

with such violence that explosions will ensue unless the ingredients are mixed with great care-best previously diluted with indifferent liquids.

Other organo-metallic bodies, such as those of mercury, may be employed, but halogen acids must then be used in place of water, this latter not altering them : CnH2n+1 +C2H2n+2•

Hg CH2n+1

CnH2n+1+ HCl=Hg ci

Cl

The halogen atoms in the haloid salts of the mono- and polyvalent alcohol radicals can be substituted by hydrogen in various ways, as by action of zinc and hydrochloric acid in alcoholic solution :

CnH2n+1 Cl+Zn+HCl=CnH2n+2+ZnCl2.

The iodides of the alcohol radicals suffer such decomposition most readily. They are decomposed by heating with zinc and water to about 200°:

2CH2n+1I+2Zn+20H,==Zn(OH)2+ZnI2+2CnH2n+2;

as also by long heating with concentrated hydriodic acid to 200°-300°:

CnH2n+1I+HI=C2H2n+2+I2

CnH2n12+2HI=C2H2n+2+212.

Instead of first preparing the iodide from the alcohol, the latter can be decomposed directly by hydriodic acid :

CnH2n+1OH+ 2HI= CnH2n+2 + OH2 + I2.

It appears generally that by action of saturated hydriodic acid solution, all organic oxides are converted into the corresponding paraffins :

C2H2O+4HIC2H6 + H20 + 212

=

C2H4O2 + 6HI= C2H6 + 2H2O + 312.

By most of the methods previously mentioned the paraffins are formed as the hydrides of the alcohol radicals, and they are frequently referred to as such.

The unsaturated hydrocarbons are also converted into paraffins by hydriodic acid, hydrogen being taken up and iodine separated:

The salts of organic acids yield paraffins when fused with alkalies, with partial splitting off of carbon as carbonate:

CnH2n+1.CO.OK + HOK = K2CO3 + CnH2n+2,
CnH2n(CO.OK) 2 + 2HOK = 2K,CO3 + CnH2n+2, &c.

150. Methods with Synthesis of Carbon Nuclei.-These consist without exception of methods in which the elements in combination with hydrocarbon nuclei are withdrawn by substances having a stronger affinity for them, whereupon the several hydrocarbon nuclei unite at the moment of liberation and form new molecules. The general type of reaction thus occurring is that known as double decomposition, as by action of the iodides of the alcohol radicals upon the corresponding zinc compounds:

or by the employment of the zinc compound of one radical with the

iodide of another:

A similar result is obtained when the iodide or bromide of an alcohol radical, dissolved in an indifferent liquid-ether, &c.—is heated with potassium or sodium :

When obtained by the last two methods the paraffins appear as the compounds of two similar or different alcohol radicals.

Another method belonging to this class is the decomposition of aqueous solutions of salts of organic acids by the electric current, whereby carbonic anhydride and the paraffin appear at the positive pole, and hydrogen and solution of the carbonate at the negative :

CnH2n+1

+ H2

CnH2n+1

2CH2n+1.CO.OK+ H2O = K2CO3 + CO2 + |

2n+1•

(Methylic hydride, carbonic tetrahydride.)

151. Methane is invariably formed by the spontaneous decomposition of organic bodies out of contact with air, i.e. during their putrefaction, and therefore occurs in the slime of marshy waters in large quantity (marsh gas), very frequently in coal mines (fire-damp.) At some places it streams in large quantity from the ground-e.g. at Baku on the Caspian Sea, where it has burnt since a very remote period.

Mixed with other hydrocarbons it is formed by the dry distillation of most organic bodies, and therefore occurs in coal gas.

To prepare perfectly pure methane, zinc methyl is decomposed by

water:

Zn(CH3)2 + 2H2O ± Zn(OH)2 + 2CH3.H or 2CH.
Methylic hydride.

It is obtained nearly pure when an intimate mixture of sodic acetate with double its weight of soda lime is heated strongly :

It can be prepared indirectly from its elements in two wayseither by passing a mixture of sulphuretted hydrogen and carbonic disulphide vapour over glowing copper, which removes the sulphur from both compounds :

CS2+2SH2+ 8Cu= 4Cu2S + CH1;

or by action of sodium amalgam on carbonic tetrachloride in presence of water:

CC1, +4Na2+ 40H2 = 4NaCl + 4NaOH + CH1.

Methane is a colourless, odourless gas of sp. gr. 5598; it is slightly absorbed by water. It burns readily with a feebly luminous flame; mixed with the requisite quantity of oxygen (double its volume) or atmospheric air, it explodes on ignition with great violence (firedamp):

Although it does not support respiration, it is destitute of poisonous qualities. Under the influence of high temperatures-e.g. when passed through white-hot porcelain tubes, or when submitted for a long time to the action of the electric spark-it is partly decomposed, with increase of volume, into hydrogen and carbon :

CH1 = C + 2H2.

When mixed in the dry state with chlorine, it is not affected in the dark; by heating, however, or by exposure to light, it undergoes changes whose amount depends upon that of the chlorine present.

A mixture of one volume of methane with two volumes of chlorine explodes powerfully on exposure to direct sunlight, carbon being deposited, and hydrochloric acid gas formed:

CH,+2C12C + 4HCl.

If the gases be mixed in equal volumes, and exposed to diffused daylight, substitution of one hydrogen by one chlorine atom takes place, and monochlor-methane or methylic chloride results :

Larger quantities of chlorine by slow action-best and with least

danger if diluted with large quantities of carbonic anhydride-yield higher chlorine substitution-products:

CH,+2C1, = 2HCl + CH2Cl2

(dichlor-methane, or methylene dichloride),

CH, +3C12=3HCl + CHC1, (trichlor-methane, or chloro

and lastly

form),

CH, +4C12=4HCl + CC1, (tetrachlor-methane, perchlormethane, or carbonic chloride).

In the presence of water, chlorine decomposes methane, slowly but completely, into hydrochloric acid and carbonic anhydride:

CH1 + 2H2O + 4C12 = 8HCl + CO2.

4

Ethane, C2H6.

CH

Ethylic hydride, C2H,H. Dimethyl,

152. Ethane is obtained, as ethylic hydride, from zinc ethyl and water:

Zn(C2H5)2 + 2H2O = 2C2H6 + Zn(OH)2;

by heating ethylic iodide with zinc and water to 150° :

2C2H2I + 2Zn + H2O = ZnI2 + ZnO + 2C2H6;

and by action of strong hydriodic acid upon ethylic iodide under the influence of high temperatures:

C2H2I + HI= C2H6 + I2.

From hydrocarbons poorer in hydrogen, as from ethylene (C2H,) and acetylene (CH2), it is obtained by the same reagent at 250° :

C2H1 + 2HI = C2H6 + I2

C2H2+ 4HIC2H6 + 212.

As dimethyl it is formed by heating methylic iodide with zinc or molecular silver in closed tubes at 150°:

2CH2I + Ag2 = Ag2I2 + C2H6;

and at the same temperature from zinc methyl and methylic iodide : Zn(CH3)2 + 2CH2I = ZnI2+2C2H6.

On opening the closed tubes it is evolved with great violence. By the electrolysis of potassic acetate in concentrated aqueous solution, it is evolved, together with carbonic anhydride, at the positive pole:

CO + H2O = CH3 + CO2 + CO(OK)2 + H2.

OK