NOTES ON ACETYLMETHYLCARBINOL JAMES R. POUND AND ALLAN M. WILSON The School of Mines, Ballarat, Australia Received January 6, 1056
The N. V. Nederlandsche Gist-en Spiritusfabriek, Delft, Holland, has recently marketed acetylmethylcarbinol or acetoin, CHs CO CH(OH)CHI, a slightly yellow liquid which changes spontaneously into a white crystalline polymer. The authors have to thank the above company for a sample of acetoin, which they have examined briefly, since the literature (1, 2, 3, 4, 5) indicates that the polymerization is incompletely understood. The authors’ samples of acetoin were obtained by melting or distilling the original solid polymer. Samples were kept at various temperatures, portions were withdrawn from time to time, and the refractive indexes were determined at 20°C.; typical results are given in tables 1 and 2. The initial value of n varied with the conditions of melting or distilling; the minimum may be 1.4175. At 100°C. and 130°C. the acetoin became browner and more viscous and developed a “burnt sugar” odor. Evidently molecular complexity (polymerization) occurs on keeping the liquid acetoin; the polymer however does not accumulate in the liquid, but forms the solid polymer. Acetoin, kept in an open beaker in the air, absorbed water; n fell from 1.4186 to 1.4141 in five days. When acetoin was kept over sulfuric acid, the value of n rose to 1.4435 in seven days, but the acetoin volatilized into the acid, darkened it, and formed a substance of sharp odor. The densities and viscosities of acetoin kept at 30.0”C. were determined, and the results are given in table 2. These properties varied similarly to the refractive index, but to a greater degree. By extrapolation, the freshly distilled acetoin would have d!? = 0.9860 and q3Oo = 0.0175. The density of acetoin is lowered (by about 9 parts in 1000) after boiling, i.e., depolymerization occurs on heating. The normal freezing point of acetoin was at -72”C., ie., it repeatedly froze and melted at this temperature. The following vapor pressures of acetoin were found by the, static method: 162 mm. at 0°C.; 164 at 10°C.; 168 at 20°C.; 174 at 30°C.; 183 at 40°C.; 210 at 60°C.; 256 at 80°C.; 330 at 100°C.; 449 at 120°C.; 664 at 140°C.; 760 at 144°C. A t ordinary temperatures the acetoin deposited crystals of the polymer in from two t o nine days. The polymer was slightly soluble in water, 1135
1136
JAMES R. POUND AND ALLAN M. WILSON
methyl and ethyl alcohols, cyclohexanol, acetone, ethyl acetate, acetic acid, and paraldehyde, and sparingly soluble in ether, benzene, carbon tetrachloride, ethylene bromide, bromoform, and acetophenone. The
TABLE
1
The change of refractive index, ngol of acetoin with time
A G E OF SAYPLB
sample 1 Distilled sample Melted tt room temper- Melted sample 2 vIelted Sam le 3 Melted aam le 4 2 at -10°C. at 30°C. at IOOY! at 130'2 ature days
. o 1 2 3 4 5 6 7 15 20
1.4192
1.4187*
1.4190*
1.4178 1.4191 1.4202 1.4205* 1.4207* 1.4208"
1.4184 1.4203 1.4199 1.4202 1.4201 1,4200 1..4204 1.4200 1.4201
1,4205 *
1.4199*
1.4186 1.4198 1.4211
1.4186 1.4247
Cooled 1.4278 1.4421 1.4546 1.4762
1.4254 1,4278 1.4312 1.4328 1.4471
* Denotes that crystals are present in the sample. TABLE
2
The change o j properties of acetoin when kepi at 80°C. MELTED SAMPLE 2
DISTILLED SAMPLE
1
DISTILLBD SAMPLE
2
A 0 1 OF SAMPLE n200
d:c
1 hr. 2Qhrs. 21 hrs. 26 hrs. 50 hrs. 4 days 5 days 6 days 7 days 12 days 16 days 29 days
0.9889
D
0.9949
0,0208
0.9980
0.0211 0.0212
0.9865 0.9878 0.9930 0.9934 0.9938 0.9938
0.0213
0.9939
0.9861
0.0178
0.0180 0.0187 0.0207 0.0209 0.0211 0.0211
1.4198 1,4200 1.4199
0.0212
1.4201
1.4192
0.9950 0.9944 0.99515 0.99515 0.9952
1.4198 1,4205
polymer was appreciably vohtile at room temperatures; if it held traces of liquid acetoin, it liquefied and volatilized more rapidly. The pure wellcrystallized polymer may be kept unchanged for several months, either in
NOTES ON ACETYLMETHYLCARBINOL
'
1137
closed vessels or between watch-glasses. The crystals are flat, monoclinic, transparent prisms, smooth and greasy to the touch, and of density 1.26. Many melting-point determinations were done on this polymer. The crystals tended to become opaque at 6O-llO0C., and they melted at 110128"C., and in rare cases at 150-160°C.;the general melting point was about 124°C. The crystals also sublimed rapidly at 15O-16O0C., and less rapidly at 100°C.and lower temperatures. The melting point depended on the rate of heating, on the time the sample was held a t a given temperature, and on the use of an open or closed tube; the results hint that a chemical change (polymer -+ liquid) is involved. This polymer then has no simple or definite melting point; it passes to liquid acetoin at any temperature and perhaps at lower temperatures, in longer or shorter times. above 30"C.,
DAYS
FIQ.1 FIQ. 1. VARIATION OF THE PROPERTIES OF FIQ. 2. CRYSTALSOF THE POLYMER
. By dilatometer experiments the transition temperature between the polymer and liquid acetoin was placed at 16'C.; but in entire absence of the liquid the solid was stable at higher temperatures (V.S.). By the cryoscopic method the polymer was found to be monomolecular in water, acetic acid, and paraldehyde. I n contact with zinc at - 10" to 0°C.acetoin became solid within twentyfour hours; the crystals appeared to be the same as before, and they too were monomolecular in the above solvents. Acetoin was kept by itself for eighteen days at temperatures between -20" and 0°C.; crystals appeared on the fourth day, and about one-third of the sample had crystallized at the last. These crystals, C, had the same form and density as the polymer, H, deposited at room temperatures. The authors thank Mr. Yates for the following notes and figure 2 about
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JAMES R . POUND AND ALLAN M. WILSON
these crystals:-"Three crystals of each substance, C and H, were sketched as seen under the microscope, and their angles on the clino-pinacoidal face were measured. All the crystals were practically identical; they had tabular habit, being very thin in the direction perpendicular to the clinopinacoidal face, b ; their interfacial angles were similar; the symmetry was monoclinic, though the departure from rhombic symmetry was only about 1'. The ortho- and basal-pinacoid faces are a and c, and d is the orthodome €ace." (1) (2) (3) (4) (5)
REFERENCES BERQMANN AND LVDEWIQ: Brit. Chem. Abstracts 126, I, 490 (1924). DIELSAND STEPHAN: Brit. Chem. Abstracts 92, I, 1000 (1907). DIRSCHERL AND BRAUN: Brit. Chem. Abstracts 1930, 454. KLING:Brit. Chem. Abstracts 88, I, 504 (1905). PECHMANN AND DAHL: Brit. Chem. Abstracts 68, 1234 (1890).
