THE HEAT OF FORMATION OF TETRAVALENT OXYGEN COMPOUNDS BY D. MCINTOSH
When organic bodies containing oxygen are added to the liquefied halogen hydrides additive compounds are formed and a large amount of heat is evolved.' In a paper on the " Higher Valencies of Oxygen," Archibald ' and McIntosh2 called attention to this, and in several instances, used the heat development to determine when the affinity of the acid was balanced by the oxygen compound. In the following pages I shall give a few measurements of the heat evolved during these reactions, and as heat evolution generally denotes chemical combination, the figures given may perhaps add something to the evidence in favour of the formation of tetravalent oxygen compounds.
Apparatus and Method The apparatus used is shown in the figure and consists of a small Dewar test-tube, A, closed by a rubber stopper through which passes the tube B and an arm of the three-way tap C. The tube B has a glass point melted in at D, so that a small sealed bulb, E, containing the organic liquid used in the experiment may be held there, and is closed by a stopper carrying the stout glass rod F. G is a stirrer formed from a platinum wire to which is attached a glass tube, and a soft iron rod enclosed in glass; by aid of a small electro-magnet, this stirrer may be pulled up as often as desired without disturbing the bulb E. The whole apparatus is surrounded by a large vacuum tube containing a paste of solid carbon dioxide and ether. The heats of formation of the hydrobromic acid salts of methyl alcohol, acetone and ether were measured in this apparatus. The organic liquids unite with hydrogen bromide, *
a
Walker, McIntosh and Archibald: Jour. Chem. SOC.,85, 1098 (1904). Ibid., 85, 9x9 (1904).
I 68
D . McIntosh
giving the compounds CH,HO.HBr,' C,H,0.HBr2 and C,H,,O.HBr. These additive bodies are white crystalline substances with low melting-points and dissolve in liquid hydrobromic acid with a heat evolution so small that it is difficult
t o measure. The heat of solution of a gram molecule of these hydrobromic acid salts is probably not larger than two or three kilojoules. In performing an experiment A was filled with liquid to h, and B with hydrochloric acid (boiling-point -83') hydrobromic acid (boiling-point -68') to j . The bulb E containing a weighed quantity of the organic liquid was placed in position and all stoppers were tightly inserted. The stirring was begun and the amount of hydrochloric acid evaporated in a given time determined by the increase in weight of a ,Geissler bulb containing potash, the acid passing through mercury before being absorbed. (This evaporation of acid is referred to subsequently as " natural evaporation".) Then another Geissler tube was attached, the bulb E broken by the glass rod F and the liquid was stirred a t the same rate as in a
Jour, Am. Chem. Soc., 27, 26 (1905). Archibald and McIntosh: loc. cit.
Formation of Tetravalent Oxygen Compounds
I 69
the measurement of the " natural evaporation." The difference in the amounts of acid vaporized gave the evaporation due to the reaction, and from the latent heat of vaporization of hydrochloric acid (previous paper) the result is easily calculated in mechanical units. I might add that it is necessary to keep the vessel containing the organic liquid above the surface of the acid, and to mix slowly, for if the reaction be allowed to take place rapidly (with E at the bottom of the tube B) the pressure developed may become great enough to shatter the apparatus. An example will make the method of calculation clear. Heat of formation of methyl alcohol hydrobromide
1 I
Time in Evaporaminutes tion
1
I
-I
Natural evaporation Alcohol added 0.077~ Natural evaporation Alcohol added 0.1160 Natural evaporation
I
Rate per minute
Mean
~
Due to alcohol
I
5
0.170 g
8
5
0.637 0.207
7 7
0.771 0,235
0.0340
\
-- /
0.0412
\ 0.0406 - /
0.487
0.0401
In the first case 0.336 of a gram of hydrochloric acid is vaporized by the combination of 0.0770 of a gram of alcohol with hydrobromic acid. The heat of formation of a gram molecule of the sale is therefore I
H = 0'336
.
32
0.0770 x 36.5
X 14.8X
IO'O
ergs = 56.6 X
IO'O
ergs.
The results are: Methyl alcohol: 56.6, 54.5, 59.3 X IO" ergs. Acetone : 56.5, 58.5, 60.9,67 X IO" " Ether: 90.0, 83.2, 115.3 x IO" " The agreement of the numbers is not wholly satisfactory, but as the carbon dioxide used is costly, I have not attempted t o obtain more exact results. Moreover, an approximate value of the heats of formation is sufficient for any theoretical
170
D. McIntosh
deductions that may be made. The figures are probably correct to IO percent, and we may write CH,HO
+ HBr = C H , H d H
-k 5 7 J
\Br
(CH,),CO
4- HBr
= (CH,),CdH
\Br /H
+ 60 J
while the energy equation for the neutralization of potassium hydrate with hydrobromic acid is + +L -
KOH
+ H’Br =. KBr + H,O + 5 7 . 3 5.
The heat development in the experiments described above is large but many acids entering into solution give equally great amounts. Thus for hydrobromic acid we have HBr
+ aq. = HBraq. + IOOJ.
In this case no compound is known to exist in solution and it may be urged that the heat evolved in the experiments described in this paper, is due merely to the heat of solution of the organic body in the acid That the compound formed dissolves with only a slight heat evolution does not affect this view, since Berthelotl has shown that during the solution of potassium hydroxide in water, nearly all the heat is developed in the formation of the hydrate KOH2H20, and that this body dissolves a slight heat absorption. However the additive products formed from the acids and organic oxygen compounds are so essentially different from the so-called molecular compounds-salts with water of crystallizationthat I shall, for the present, regard the heat developed as due to the f o r m a t i a o f compounds in which oxygen functions as a tetravalent d&ent. McGill University, Moatreal. December, I 907.
