[CONrRIBcTIOh
Vol. 79
C;. K. HELMKAMP, F. L. CARTERAND H. J. LUCAS
1300 NO. 2121
FROM THE GATE? AUD
CRELLIN LABORATORIES O F CEIEMISTRY, CALIFORSIA IYSTIlUTC
OF
TECHVOLOGY]
Coordination of Silver Ion with Unsaturated Compounds.
VIII.
Alkynes]
BY GEORGEI(.HELMKAMP, FORREST L , CARTER AND HOWARD J. ILJCAS~ RECEIVEDSEPTEMBER 4, 1956 Quasi thermodynamic equilibrium constants, K,, of the reactions of aqueous silver nitrate with a number of alkynes have been determined by solubility measurements at ionic strength p = 1 and in the absence of oxygen. Whereas 4I-I c:tlculated with K I has the respective unrealistic values of 0.0 and +6.8 kcal. for 3-hexyne and 2,2,5,5-tetramethyl-3-hexyne, the respective AI€ values are -4.3 and -5.0 kcal. when calculation is made with K,. In 3-hexyne and its a-methyl hoinologs the value of Ra is reduced to about one third for each substitution of a n a-hydrogen atom by a methyl group.
The ability of 3-hexyne t o complex with silver and back titration with standard silver nitrate, nitrate, as determined by a distribution m e t h ~ d , ~chromate being the indicator.6 is approximately that of an alkene, for it is someThe sample for alkyne analysis is run into an what greater than t h a t of a trans-hexene and some- appropriate volume of especially purified3 carbon what less than that of a cis-hexene. The solubility tetrachloride' and 5 M potassium cyanides a t about method of Andrews and Keefer4is much more rapid IOo in a grease-free mixing cylinder. After this than the distribution method and was adopted for has been shaken mechanically for 0.5 hour the the investigation of other alkynes. However, we phases are separated and the organic phase is dried with magnesium sulfate. From measurement of interpret our results in a different way. So lar, only hydrocarbons have given satisfactory the intensity of the C-H band at about 3.4 p the results. a-Halogenated alkynes are reactive with concentration of alkyne in the carbon tetrachloride silver ion, a-hydroxy alkynes are oxidized and phase is determined. The concentration of alkyne rr-carbonyl alkynes are not stable under the condi- in the aqueous phase a t p = 1 is calculated. Data.-These a t 23" are given in Tables I to tions employed, presumably due t o reactivity with VI, respectively, for 3-hexyne, I ; 2-methyl-:?water. The Method.-The alkynes were distilled and TABLE I stored under 99.9% n i t r ~ g e n . ~Some, as for ex1 I N AQUEOUSSILVER SOLUBILITY OF 3-HEXYSE, 1, AT p :miplc I -hutyne, were stored in sealed ampoules. sI'I'KATR An ampoule of alkyne is placed in an equilibra(&I+), (Unt), (Agi +). (Unt), M M x 106 .M M X 10' tion flask, capacity 250 ml., provided with sufficient outlets t o allow transferal of solutions under nitroAt 3 5 O At 25' gen. The flask is evacuated to less than 1 mm. of 68 0.000 64 0 .000 mercury, nitrogen is admitted to atmospheric pres199 ,074 129 ,108 sure, and the operation is repeated. The ampoule 233 .190 244 .128 is broken by swirling or shaking. Sufficient oxy.272 405 .307 361 gen-fret 1 AT silver nitrate and/or 1 M potassium 47s .360 408 .318 nitrate are separately forced into the flask t o give 496 ,548 610 ,338 100 to 300 ml. of solution, ionic strength p = 1. 756 ,730 822 .531 having approximately the desired concentration of 1102 .752 843 ,761 silvcr nitrate. Sufficient alkyne is taken t o leave 1.000 1475 1.000 1135 about O..? ml. mdissolved. The flask is covered TABLE 11 with aluminum foil to exclude light. SOLUBILITY O F 2-METHYL-3-HEXYSE, 11,AT 25.0" A:K , = 0.22, and K~ = 8.2 x 10-3. Calculation of A H for the argeiitatioii reaction:< of 3-liexyne and 2,2,;?,.i-tetramethql-~-hexq-rle frorii (Un). and the values of the equilibrium constants, ICl, K 2 and K,. The K1 value, 17.3, and the K2 the K 1 values a t 2.5 and 33' gives the unrealistic value, 0.36, of 3-hexyne agree well with the respec- values of 0.0 kcal. and (3.8 kcal., respectively, from K, the realistic values of -4.5 ant1 tive values, 19.1 and 0.22, obtained by the distri- whereas 5.0 kcal., respectively, are obtained. These last bution method.3 The K , value of 13.1 X lo-? is sixteen times the KOvalue of 0.82 X ob- A H values are comparable to those of alkenes" and tained by the distribution r n e t h ~ d . ~Here KO = indicate t h a t K , is a more satisfactory constant K1. K, probably is close t o a thermodynamic l i l / K ~ ,where KD is the distribution constant of than equilibrium constant and is here designated a CTn between aqueous potassium nitrate, 1 M , and quasi equilibrium constant. Reported values of carl)ori tetrachloride. :j
'1
( I O ) 111 this treatment, t h e activity coefficient of a pure liquid is t;iken as unity. I t is assumed t h a t positive Raoult's Lam deviations occur in aqueous solutions and t h a t t h e activity coefficient of t h e liquid in :iqueous solution increases with dilution; J. H. Hildebrand a n d R . L. s r o t t , "'The Solubility of Nonelectrolytes," 3rd Ed., Reinhold P u h l . C t n p , , N e w York, PIT. Y . , 3050, p. 28 and Fig. 8, p. 33. JorJRX.41,, 60, 830 (1838). ( 1 I 1 S. W i n s t r i n and H J . T,ucns, TIEIS
(12) T h e importance of inole fractions W ~ pointed S out t o one of 1 1 hy Professor Edwin Lassettre, of Ohio State University. (13) This is because i n t h e expression for K O ,as given in e r i . 7 ,1 I:. R . Hepner, K, 'l'ruehIi)r)d and I I . J. Lucas, '1'1115 J o v R N . ~ ~ , 74, , 1338 (1852), ( E n ) , is inclu
