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listed in Table I1 are essentially the same, it may be that the corrosion rate is determined by the rate of diffusion of oxygenS to the metal surface, rather than by the rate of oxidation of the metal. This cannot be true, however, of the other four metals used, since the initial corrosion rates are considerably lower and indicate that the oxidation rate of metals is controlling. Conclusions 1-The electromotive series as ordinarily used is not the proper criterion for judging the probability of corrosion of a metal in oxygenated water. All experimental work was done under constant conditions of liquid agitation and hence the rate of oxygen diffusion through the liquid would be constant.
Vol. 23, No. 4
&The free-energy decreases, assuming oxygen and water to react with metals to form metallic hydroxides in saturated solution, are more exact measures of the tendencies to corrode. 3-Aluminum, copper, iron, nickel, silver, tin, and zinc all show finite initial rates of corrosion in oxygenated water. +-The initial corrosion rates of all metals tested decrease after a relatively short time, indicating the formation of partially or completely protective i i h s in all cases. +-Metals such as nickel, tin, copper, and silver do not seriously deteriorate on exposure to oxygenated water, not because of a negative corrosion tendency, but because of the formation of an impermeable corrosion product which prevents further deterioration.
Syntheses from Natural-Gas Hydrocarbons I-Caproic Acid from Pentane* H. B. Hass and J. R. Marshall PURDUEUNIVERSITY, LAFAYETTE, IND.
Conditions have been worked out for obtaining good HE need for a more inshown to react with potasyields of alkyl cyanides from alkyl chlorides by treattimate and extended sium cyanide yielding nitriles ment with sodium cyanide. Yields of 70 per cent knowlcdge of the (8). P r e l i m i n a r y tests with a recovery of 25 to 28 per cent of unchanged chloride c h e m i s t r y of tohe non-benshowed that a q u e o u s alcohave been obtained with normal amyl chloride. Other zenoid h y d r o c a r b o n s and holic solutions of amyl chloprimary chlorides also react satisfactorily. Secondary their immediate derivatives ride and sodium cyanide yield alkyl chlorides and bromides give poor yields (around has been frequently stressed capronitrile slowly upon re30 per cent) and tertiary amyl chloride or bromide by J. F. Norris, B. T Brooks, fluxing. The main object of gives no nitrile at all under these conditions. By the and other eminent authorithe research was to deteruse of sodium iodide, which acts as an intermediate ties. Indeed, anyone gaining mine the optimum conditions compound catalyst, the yield can be raised to 90 per cent even a slight familiarity with and yield. or more. hydrocarbon chemistry is imMaterials The hydrolysis of amyl cyanide by means of 67 per pressed by the dearth of inforcent sulfuric acid is complete in 30 minutes. mation on even the commonThe normal amyl chloride' Amyl and butyl chlorides resemble carbon tetraest reactions. With the obp. 10.5-107" C.) was ob(b. chloride, ethyl iodide, benzene, hexane, etc., in formject of contributing to fundatained by the rectification of ing binary minimum boiling azeotropic mixtures with mental chemical knowledge a sample produced by the ethanol and ternary azeotropic mixtures with ethanol within this field, the senior chlorination of natural-gas and water. author, in conjunction with pentane by the Sharples SolThese processes have been found suitable for the students, is engaged in a sysvents Corporation.2 The somanufacture of caproic acid, which is used in the tematic study of some of the d i u m cyanide was Mallincpreparation of hexylresorcinol, a well-known pharmareactions of hydrocarbons obkrodt U. S. P. IX, granuceutical. With slight modifications these methods t a i n a b l e from natural gas. lated. Other reagents were may also be used for the conversion of any primary The relatively simple paraffin of c. P. grade. alkyl chloride to the fatty acid containing one more h y d r o c a r b o n s have been carbon atom. chosen because they are Procedure readily purified, and also because recent commercial developinents have made certain inWeighed amounts of sodium cyanide, water, alcohol, and termediates readily available to investigators. amyl chloride were placed in the order named in a 500-ml. Perhaps the best known controllalk reaction to which par- Pyrex Florence flask. The flask was fitted with a reflux conaffins readily lend themselves is halogenation. Alkyl halides denser, placed on a water bath, and the contents were reare known to react with metallic cj,anides yielding nitriles, fluxed for a definite time. Shellacked cork connections were from which fatty acids, esters, amines, amides, alcohols, used throughout, owing to the tendency of rubber to absorb and other classes of compounds are readily prepared. It amyl chloride vapor. At the end of the run the flasks were might be supposed that the latter reaction had been rather removed from the bath, cooled, and fitted with two-hole thoroughly studied, but we were unable to find that any case corks containing a 100-cc. separatory funnel and a tube leadhad been reported where an alkyl chloride had been success- ing to a Liebig condenser. The flask was immersed in an fully treated with sodium cyanide to yield an alkyl cyanide. oil bath and the entire liquid contents of the flask were disButyl bromide has been converted to valeronitrile by means tilled out, water being added from the funnel to drive over of sodium cyanide reacting in aqueous alcoholic solution writers wish to thank R. R. Read, director of Chemical Re( I ) , and alkyl chlorides under similar conditions have been search2 The Laboratories, Sharp and Dohme, for a sample of especially pure
T
1
Received December 6, 1930.
normal amyl chloride which was used in most of these experiments.
the last traces of amyl c,yanide. Since this compound is practically insoluble in water, the distillation was considered complete when no drops of nitrile were observed floating upon the surface of the water dropping from the condenser. This procedure left behind sodium chloride, unreacted sodium cyanide, and traces of tar. The distillate contained amyl chloride, amyl cyanide, water, and alcohol. The distillate was treated with anhydrous potassium carbonate, which completed the separation of the water into a lower layer, the upper layer containing alcohol, amyl chloride, and amyl cyanide. The upper layer was separated, 95 per cent ethanol added to bring total volume of ethanol up to 75 cc., and distilled. The reason for adding the tkhanol at this point is that it forms a minimum-boiling :ueotropic mixture with amyl chloride, boiling a t about 72.5' C. The addition of alcohol in large excess over the composition of the constant-boiling mixture makes the complete separation of the unreacted amyl chloride from the amyl cyanide (b. p. 161-162' C.) a simple matter. When the oil bath surrounding the distilling flask was a t 110' C. and no more distillate came over, the residue was cooled, treated with water in a separatory funnel to remove traces of alcohol, dried with calcium chloride, and weighed as crude amyl cyanide. I n the experiments in which methanol was used as solvent, the methanol was first distilled off from the reaction mixture and then the above procedure followed. This was necessary because methanol does not form an aeeotropic mixture with amyl chloride. When isopropanol was used as solvent it was employed in the distillation in the same way as ethanol. Results
In Table I the amount of alcohol used was varied. the other reagents being held corlstant a t 53 grams (0.5 mol) of amyl chloride, 27 grams (0.55 mol) of sodium cyanide, and 27 grams of water. The figures refer to percentage of the theoretical yield of amyl cyanide obtained by refluxing for 48 hours. Table I-Effect
YIELDWITH VARYING QUANTITIES OF ALCOHOL
Methyl Ethyl Isopropyl
I
25ml.
50ml.
100 ml.
75 ml.
~
-
.
125ml.
%
%
%
%
%
s:2 3.7
17.6 25.5 17.6
23.75 44.5 21.0
41.5 51.2 17.6
35.7 54.9 17.6
At every concentration ethanol showed higher yields than the others. Further work was therefore confined mainly to this solvent. The results expressed in Table I1 were obtained by varying both the concentration. and amount of ethyl alcohol, other conditions remaining as before. Table 11-Effect of Varying B o t h Concentration and A m o u n t of Ethanol in Ethanol-Water Mixtures on Yield of Amyl Cyanide Y I E L D WITH V A R Y I N G
ETHANOL 75ml.
7 90 95
0
1
% 65.0 48.5 47.0 43.0
Another series of experiments proved that increasing the amount of sodium cyanide or the time of refluxing improves the yield only slightly, a maximum yield of 72.2 per cent having been obtained when a 20 per cent excess of sodium cyanide is allowed to react for 96 hours. When a temperature of 104' C. was used (pressure 50 pounds gage) a yield of 59.6 per cent was obtained in 21 hours. Other conditions were the same as in the starred result in Table 11. The yields are all based upon the amyl chloride used. I n the best runs, where from 68 to 70 per cent of the amyl chloride was converted to cyanide, it was always possible to recover from 25 to 28 per cent of unchanged amyl chloride. Effect of Sodium Iodide
Since alkyl chlorides are known to react rapidly with sodium iodide, forming alkyl iodides and sodium chloride, and alkyl iodides are known to yield alkyl cyanides rapidly when treated with sodium cyanide, a run was made using equimolar portions of amyl chloride and sodium iodide with a 10 per cent excess of sodium cyanide, refluxing with 90 ml. of 80 per cent ethanol for 24 hours. A yield of 90 per cent of crude amyl cyanide was obtained. Hydrolysis of Amyl Cyanide
This reaction may be carried out in either acid or alkaline solution, but is best accomplished by using equimolar portions of amyl cyanide and 67 per cent sulfuric acid. The mixture is placed under a reflux condenser and warmed until the exothermic reaction has started. Heat is then withdrawn until the more violent part of the reaction has subsided, after which the mixture is again warmed. At the end of 30 minutes no odor of the isocyanide is apparent and the product is entirely soluble in aqueous sodium hydroxide indicating complete conversion to caproic acid. Practically no discoloration accompanies this step. Water is added to prevent the crystallization of ammonium bisulfate and the upper layer is separated. Distillation showed it to be practically pure caproic acid.
of Varying Concentration of Alcohol on Yield of Amyl Cyanide
ALCOHOL ~
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90ml.
970 69.5* 60.5 52.0 44.5
AMOUNTSO F
SOLVENT
105ml. 125 ml. 150ml. 2 0 0 m l .
%
%
%
63.5 60.5 55.0 47.5
SOYO 53.2 49.5
56:O 52.5 46.4
47 .5
7" 40:7 37..j 31.'7
300 ml. % .36.6 28.0 20.0
These data would appear to indicate that better results might be expected with a smaller percentage of ethanol in the solvent, but data in Table I, where slightly more dilute alcohol was used, show a decrease in yield and indicate that greatly improved results could not be expected in this direction.
Discussion
The highest yields of amyl cyanide from amyl chloride were by the use of sodium iodide, which acts as an intermediate compound catalyst.
+ + +
C6H11Cl NaI +C6Hl1I f NaCl NaCN +CSHI,CNf NaI CsHllI C6HllCl NaCN +CsH1lCN NaCl
+
Two disadvantages inherent in this technic are the greater cost of the reagents and the presence in the final reaction mixture of small amounts of amyl iodide, which is not readily separated from the cyanide by distillation. The sodium iodide method is proving of value in the cyaniding of some of the more uncreative chlorides and bromides, but is hardly necessary in the case of normal amyl chloride. The yields are largely dependent upon the purity of the normal amyl chloride used. Separate experiments have established the fact that secondary amyl chlorides and bromides give poor yields of cyanides, while tertiary halides give none a t all under the conditions of these experiments. The methods described above are capable of being extended to other primary alkyl chlorides, with excellent yields. I n case the boiling point of the chloride is too low-e. g., nbutyl c h l o r i d e i t is best to use pressure above atmospheric. Iron does not interfere with the reaction, so an ordinary autoclave may be used. Literature Cited (1) Adams and Marvel, J . A m . Chem. SOC.,42, 318 (1920). (2) Lieben and Rossi, A n n . , 159, 75 (1871).
