Cooling Bath Compositions

from "The Chemist's Companion," Gordon, A. J.; Ford, R. A.; Wiley: New York, 1972

-25

T°C % o-xyl % p-xyl -35 -30 83 17 -35 75 25 -45 -40 66 34

T°C -45 58 42 -55 -50 50 50 -55 42 58 -60 33 67 -65 -65 25 75 -70 17 83 -75 0.0 0.2 0.4 0.6 0.8 1.0 volume fraction of o-xylene Figure 1 . Cooling bath temperatures for mixtures of o- and p-xylene and dry ice (from Phipps & Hume, J. Chem. Educ . 1968 , 45 , 664) Alan M. Phipps Boston College Chestnut Hill, Massachusetts General Purpose Low Temperature and David N. Hume Massachusetts Institute of Technoloqv Dry-Ice Baths Cambridge, Massachusetts 62139 - I

A great many methods have been de- is not useful since it forms a thick sludge at its melting scribed for thc preparation and maintenance of low point (-26T) but mixtures of o- and m-xylene give low temperature baths, and the field has been extensively viscosity baths with an approximately linear tempera- reviewed recently.' Among the simpler techniques, the ture dependence on composition (see figure). Analyti- liquid nitrogen-organic solvent slush bath has become cal grade acetonitrile gives a useful bath at -4Z°C, increasingly popular and a compilation of 86 such baths while temperatures between -4Z°C and -51°C are has been published by R~ndeau.~ obtainable with acetonitrile containing 0-3% acrylo- We have found it convenient to employ an even nitrile. Technical grade acetouitrile was found to give simpler bath composed of solid carbon dioxide and a reproducible bath at -46'C. Some mixtures do not organic solvents or solvent mixtures having a freezing give baths in which the temperature varies normally point above -7S°C. Solid lumps of dry ice in a with composition. Mixtures of 3-hept,anone or cyclo- Dewar flask containing one of several solvent systems hexanone with acetone act as if they were acetone-dry afford a bath of rcasonahly uniform temperature and ice baths containing the solidified higher-melting ketone. low viscosity. Such a bath is not, of course, a system at A similar result ensues for mixtures of n-octane and equilibrium; a layer of solid solvent appears to form iso-octane. over the dry ice and a steady state is obtained with Because of the simplicity of the technique, the easy slow evolution of gaseous CO1. The baths are generally availability of dry ice and its low cost, and the readiness reproducible to + 1°C if they are agitated intermittantly with which a desired temperature may be obtained, the and if only a small excess of dry ice is used (e.g., 24cc use of dry ice baths is worth consideration even where per 200 ml in a standard 265 ml (one pint) Dewar flask). equipment for handling liquid nitrogen is available. Many of the solvents cited by Rondeau may be em- This work was supported in part through funds pro- ployed, although the bath temperature is not always vided by the U.S. Atomic Energy Commission under the melting point of the solvent. Carbon tetrachlo- Contract AT(30-1)-905. ride (-23"C), 3-hcptanone (-3S0C), cyclohexanone (-46°C) and chloroform (-61°C) provide reproducible low viscosity baths at the temperature indicated. Many solvents which have appropriate melting points may be unsatisfactory because they solidify, or becon~ehighly viscous at low temperatures (c.g., n- octane, alcohols) or are noxious. Certain solvents, however, when mixed in the right proportions provide a considerable range of stable bath temperatures together with low viscosity. Of especial interest to this labora- tory has been the attainment of temperatures through- out the liquid range of ammonia (-78' to -33"C), and we have fonnd that most of this range can be covered with mixtures of ovtho and nzeta-xylene. Pure o-xylene

-80 NABSLER,J., "Experimental Techniques for Low Boiling Sol- 0 0.2 0.4 0.6 0.8 vents," Academic Press, New York, N. Y., 1966, "Vol. I.- Volume Froction of 0-rylene The Chemistry of Non-Aqueous Solvents," (Editor: J. J. LAG- OWSKI), p. 213. RONDBAU,R. E., 3. Chem. and Eng. Data, 11,124 (1966). Stecldy stole temperature of dry-ice--xylene, m-xylem mixtvro~.

664 / Journal of Chemicol Education LITERATURE CITED (3) Fulton, C.C., Zbid., 5, 27 (9153). (4) Lerner, M., Anal. Chem. 32,198 (1960). Butler, W.P., Ryan, R.L., “Methods of Analysis,” Pub. No. (1) (5) Small, L.F., Lutz, R.E., “Chemistry of theopium Alkaloids,’’ 341 (Rev, 2-60), U.S. Treasury Dept. Internal Revenue p. 154, U. S. Treasury Dept., Public Health Service, Wash- Service, Washington, February 1960. ington, 1932. (2)., Davis, T.W.C.. Farmilo. C.G., Genest, K.,’ Bull. Narcotics U. N.’Dept. Sokal Affairs 14, 47, (1962). RECEIVEDfor review July 19, 1965. Accepted October 6, 1965.

Slush Baths

R. E. RONDEAU

Air Force Materials Laboratory, Wright-Patterson AFB, Ohio

The preparation of constant temperature slush baths is described and 86 common slush baths are tabulated in order of decreasing temperature from 13” to -160” C. Some experimental applica- tions of these cooling agents are also described.

THEACCOMPANYING TABLE lists 86 common solvents and their slush bath temperatures in order of decreasing temper- ature from 13’ to -160’ C. A slush bath can be defined as a Table I. Materials for Low Temperature Slush Baths (with coolant consisting of a low melting liquid which has been parti- Liquid Nitrogen) ally frozen by mixing with liquid nitrogen. It is prepared by slowly pouring liquid nitrogen into a Dewar flask containing Solvent Tcmp., C. Solvent Temp., “C. the solvent while continuously stirring the mixture until the p-Xylene 13 +lo Ethyl acetate - 84 desired consistency is obtained. When properly mixed, the con- p-Dioxane 12 n-Hexyl bromide -85 sistency of the crystallized solvent is that of a fluid slush which Cyclohexane 6 Methyl ethyl ketone -86 will maintain a constant temperature as long as the bath is Benzenc R Acrolein - 88 kept slushy by occasionally blending in more liquid nitrogen. Formamide 2 Amyl bromide - 88 Rondeau and Harrah (2) made use of an ethyl bromide Aniline -6 +Butanol a - 89 slush bath in measuring the melting point of 3-hexyne. The Diethylene glycol 5 - 15, s-Butanol - 89 temperature rise 01 this particular slush was approximately Cy cloheptane - 12 Isopropyl alrohol a -89 0.2’ C. per minute when left standing at room temperature in Methyl benzoate - I2 Nitroethane - 90 Benzonitrile -13 Heptane -91 an uncovered 47 X 125 mm. Dewar flask. Benzyl alcohol - 15 %-Propyl acetate - 92 With certain solvents, such as diethylene glycol and some of Propargyl alcohol - 17 2-Nitropropane - 93 the alcohols, a heavy sirup is formed. Although not a5 conven- 1,2-Dichlorobenzene - 18 Cyclopentane - 93 ient to handle, a viscous bath is still useful for cooling purposes. Tetrachloropthyleue -22 Ethyl benzcne -94 The solvents in Table I that form a highly viscous coolant have Corbon tetrachloride -23 Hexane - 94 heen marked with an asterisk. 1,3-Dichlorobenzene - 25 Toluene - 95 The temperatures listed in the table are given to the nearest Xitromcthane - 29 Cumene - 97 degree centigrade. Measurements were made with a calibrated o-Xylene - 29 Methanol - 98 toluene thermometer for temperatures above -95’ C. and Bromobenxene - 30 Methyl acetate - 98 Iodobenmie -31 Isobutyl acetate - 99 with a calibrated pentane thermometer for readings below nt-Toluidine - 32 Amyl chloridc - 99 -95’ C. All of the solvents used were reagent grade chemicals. Thiophene - 38 Butyraldehyde - 99 In general, the purer the compound, the narrower its dush .hetonitrile - 11 Propyl iodide -101 bath temperature range; however, the variation in temperature Pyridine -42 Butyl iodide - 103 with purity has not been studied. Benzyl bromide -43 Cyclohexene - 104 Slush baths are especially useful in degassing liquids and Cyclohexyl rhloride -44 s-Butyl amine - 105 fractionating mixtures. Ir‘ewton (1) has desigr.ed a low tempera- Chlorobenzenc - 45 Isooctane - 107 ture reflux condenser in which the liquid can he refluxed under m-Xylene - 47 1-Nitropropane - 108 n-Butyl amine - 50 Ethyl iodide - 109 vncuum at a temperature where its vapor preqsure is negligible. Benzyl acetate - 52 Propyl bromide -110 The method requires the use of a constant temperature cooling n-Octane - 56 Carbon disulfide -110 bath to maintain the desired temperature. The convenience Chloroform - 63 Butyl bromide -112 of a table of slush bath temperatures in using such a technique Methyl iodide - 66 Ethyl alcohol Q - 116 is readily apparent. tert-Butyl amine - 68 Isoamyl alcohol Q -117 Volatile mixtures can be separated in a vacuum system by Trichloroethylene - 73 Ethyl bromide -119 fractional condensation through a series of three traps cooled Isopropyl acetate -73 Propyl chloride - 123 to successively lower temperature. Here again, the judicious o-Cymene - 74 Butyl chloride - 123 selection of the proper slush bath temperature determines the p-Cymene - 74 Acetaldehvde - 124 Butyl acetate 77 Methyl r&lohcxane 126 efficiency of the separation. - - Isoamyl aretate -79 n-Propanol 5 - 127 Acrylonitrile - 82 n-Pentane -131 LITERATURE CITED n-Hexyl chloride -88 1,5-Hexadiene - 141 Propyl amine - 83 i.w-Pen tane - 160 (1) Newton, AB., Anal. Chem. 28, 1214 (1956). (2) Rondeau, R.E., Harrah, LA., J. CHEM.ENQ. ~)ATA 10, 84 (1965). a High viscosity slush. RECEIVEDfor review April 20, 1965. Accepted September 16, 1965. -

194 JOURNAL OF CHEMICAL AND ENGINEERING DATA