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IiVD CSTRIAL A N D ENGINEERING CHEMISTRY
VOl. 18,Yo. 8
The Aliphatic Tertiary Alcohols and Their Industrial Possibilities' By Harold S. Davis and Wallace J. Murray ARTHURD. LITTLE,INC.,CAMBRIDGE, MASS.
LIPHATIC tertiary alcohols are now being manufacA t u r d by processes developed in this laboratory, the raw material being the olefins Produced in quantity from petroleum by a new type of cracking process. This represents part of a program for a better economic utilization of this great resource by the production of a greater diversity of high-grade products. The boiling points of tertiary butanol, the lowest member of the series, and of tertiary amylol, the next member, are about the same respectively as of ordinary ethyl alcohol and normal propanol. The tertiary series is as complete as the primary series of alcohols, except that there is no member corresponding to methanol.
These tertiary alcohols differ notably in solvent power from the primary alcohols. For example, they offer unique possibilities for use in recrystallization processes. Their chemical properties are also unique. They resist oxidation and the action of halogens. Their hydroxyl group is one of the most labile among organic compounds, and this fact makes possible many interesting syntheses. Their physiological properties have only been slightly investigated; the tertiary group seems to be related to such phenomena as Odors hypnotic effect*and perhaps even vitamin power.
. . ... . . . , . . . .
ERTAIN tertiary alcohols occur in nature in essential oils, but only those having ten or more carbon atoms. Those lower members of the series which are known have all been made by synthetic methods and have been for the most part chemical rarities. Four years ago tertiary butanol was sold by a well-known American firm in small quantities at a rate corresponding to about $476 per gallon. It is pleasing to state, however, that since early in 1925 these substances have been available a t reasonable prices because it has been found that tertiary butanol and many of its homologs can be suitably prepared from petroleum products. The details of this work are not relevant to the present paper. Briefly, however, we are able to change olefins produced in certain types of cracking processes directly into tertiary alcohols through the intervention of catalysts or via intermediate chlorides. The liquids of a whole series thus become available to industry. They are similar in many physical properties to ordinary alcohol and its homologs, but their chemical properties, solvent powers, and physiological effects are entirely different.
C
Physical Properties
The boiling point and density of tertiary butanol are nearly the same as those of secondary propanol (isopropanol) or primary ethanol (ordinary ethyl alcohol), and the rule is somewhat general that these properties of a tertiary alcohol are similar to those of the homologous secondary alcohol with one less carbon atom, or of the primary alcohol with two less carbon atoms. To a'certain extent their solubilities in water follow the same rule, but no such similarity exists regarding the refractive indices or the freezing points of the three types of compounds. Table I shows these relationships. The closeness of the boiling points of the three members of group I is especially striking and indicates the impossibility of separating tertiary butanol, isopropanol, or ethyl alcohol from one another by fractionation. While ethyl alcohol freezes a t -114' C. and isopropanol a t -85.6' C . , tertiary butanol freezes a t 25.5" C.-that is, a little above room temperature. It forms lustrous needles which we have often obtained a t least 6 inches long. This remarkably high freezing point of an alcoholic substance Presented before the joint session of the Division of Petroleum Chemistry a t the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926. 1
which is probably related to its compact structure should be of cdnsiderable utility for special cases. Solvent Properties-Utility
for Recrystallizations
The molecular. structures of all the tertiary alcohols are more compact than those of the isomeric primary or secondary ones. I n consequence their solvent powers are quite different. The tertiary alcohols should present unique means for purifying certain substances-for example, the hydroxy acids, by recrystallization from hot solutions. For this purpose a solvent is needed in which the substance is not very soluble a t ordinary temperatures, but in which its solubility increases as rapidly as possible with the temperature. The potential utility of the tertiary alcohols for this purpose may be illustrated by a comparison of tertiary butanol, ethyl alcohol, and water as solvents for citric acid (Figure 1). It appears that from this point of view tertiary butanol is by far the superior solvent for recrystallizing citric acid. P r o p e r t i e s of Lower A l i p h a t i c Alcohols Boiling Refractive Approx. solubility p:int Density index at Group Alcohol C. 2Oo/4OC. 20" C. in water I Tertiary butanol 8 2 . 5 5 0.7887 1.38779 Miscible Constant boilinn 1 mixture (88.24% 79.9 tertiary butanol, 11.76y0 water) Miscible 1.37757 82.28 0.7887 Secondary propanol Constant boiling (87.9% mixture secondary propanol,l2.l%water) Miscible 1.36232 Primarv ethanol 7 8 . 3 2 0.7894 1 vol. in 8 1.4052 0.8093 101.8 I1 Tertiary pentanol 1.3974 1 vol. in 8 0.8078 Secondary butanol 99.5 (at 150 C ) '-i,-3-854-., Miscible Primary propanol 97.2 0.8035 I11 Tertiary hexanol (straight chains) 123 0.824 Secondary pentanol 115.6- 0 , 8 1 9 1.4077 1 vol. in 6 (straight chains) 119.5 0.808 1.4043 (at 2.5' C.) Primary butanol (straight chains) 117.7 0.809 1.3993 1 vol. in 11 I V Tertiary hexanol (forked chain) 117.6 0.839 Secondary pentanol 112.5 0.833 (forked chain) Primary butanol 106.5 0.817 (forked chain) T a b l e I-Physical
~
~~~
~~
1
1
J
Chemical Properties
The chemical properties of the tertiary alcohols are entirely different from those of the ordinary alcohols with which in-
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I N D CXTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
August, 1926
dustry is familiar. This may be traced back to the fact that every tertiary alcohol contains an hydroxyl group linked t o a carbon atom which is also united to three other carbon atoms; thus CR3
I
RaC-C-OH
I
CRa
Apparently, the valencies of the central carbon are largely saturated by the other three carbon radicals so that the C-(OH) bond is weak. Since this union is weak the 0-H bond is abnormally strong. The following unique properties of the tertiary alcohols can be understood with these assumptions.
Ease of Replacement of the Hydroxyl Group The hydroxyl group of the tertiary alcohols is one of the most labile of all groups in organic compounds. For instance, when tertiary butanol is mixed with concentrated hydrochloric acid it goes over to tertiary butyl chloride, wliich separates as a top layer in a few minutes. The transformation to chloride is even more rapid in the case of tertiary amylol. This reaction sharply differentiates the tertiary alcohols from the saturated secondary and primary alcohols of the aliphatic series, and in the case of the lower boiling alcohols a t least it can be utilized to determine quantitatively the tertiary alcohols in mixtures. s 80 P 4
B $,
70
60 50
2
40
c
T
c
€FFECT OF T€MP€RA TURE ON THE S O l U B / i / T Y Of C/TR/C ACJD I N
30
\5 2 0
8
IO
IO
20
30
‘$0 50 60 TkMDERATURE- DfGREES C
“0
50
90
100
Figure 1
The lability of the hydroxyl group is inherited by the halogen radical which displaces it. Undoubtedly, the tertiary alcohols and their halides offer great possibilities in organic syntheses for introducing hydrocarbon radicals with branched chains into compounds.
Ease of Dehydration-Polymerization The tertiary alcohols can be dehydrated with great ease. If mild agents such as oxalic acid or even its solutions in water are used, good yields of the corresponding olefins can be obtained, which contain two radicals linked to an unsaturated carbon atom. For instance, tertiary butanol with oxalic acid gives a good yield of isobutylene. With stronger agents part of the olefin is changed to the di, tri, or higher polymer. Thus, if the alcohol is distilled from sulfuric acid, the relative proportions of the olefin and of its different polymers in the products vary with the quantity and strength of the sulfuric acid and with the conditions of distillation. r o w that the alcohols are available, the exact (conditions for getting the maximum yields of the simple olefins and of their different polymers should be worked out. This would give supplies of a large number of higher olefins with branched chains in a comparatively pure state. Tertiary butanol alone will give di-isobutylene (an octylene), tri-isobutylene (containing 12 carbon atoms), etc. Each of the alcohols will give different polymers, and there is also the possibility of making mixed polyrners from two alcohols, a field which has been scarcely touched.
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As soon as the experimenter can buy or prepare for himself a t moderate cost kilogram quantities of these different olefins, there will be interesting industrial possibilities to test. For instance, it has been claimed that olefins can be particularly useful in synthetic lubricating oils. Their individual antiknock properties in gasoline should also be tested out. Organic compounds with branched chains often possess peculiar and useful properties. Thus the substitution of the tertiary butyl group in certain nitro derivatives of aromatic compounds produces substances with a strong musklike odor, and artificial musk is actually made in this manner.*
Resistance to Oxidation Another outstanding property of these alcohols is their resistance to oxidizing agents. This is probably due to the fact that oxidation must break the carbon chain, whereas in the case of primary and secondary alcohols the first step in oxidation leaves the chain intact. For instance, primary and secondary alcohols react explosively with chromic anhydride, yielding aldehydes, ketones, and other products. On the other hand, chromic anhydride can be added in small lots to a limited quantity of tertiary butanol with complete safety. It rapidly dissolves t o give a reddish solution and if the excess of tertiary butanol is removed by standing over sulfuric acid in a desiccator, there remains a blackish solid corresponding in weight t o a compound of one mol of the alcohol with one of the anhydride. (Care must be taken not to pour tertiary butanol on a large quantity of chromic anhydride or to heat up large quantities of the solution or of the solid compound, since violent explosions can occur.) This reaction of tertiary alcohols with chromic acid was first noticed by W e i n h a u ~who , ~ investigated the behavior of representatives of the aliphatic, aromatic, and hydroaromatic groups. He showed that esters are formed with the chromic acid and developed from this fact a useful method for the detection of tertiary alcohols in their mixtures with either primary or secondary ones: If a solution of the substance in carbon tetrachloride or petroleum ether develops a pure red color when shaken with aqueous chromic acid and allowed to stand a long time, there is no doubt of its tertiary nature. If the solution rapidly discolors it is of course not wholly proven for primary and secondary alcohols always, and tertiary alcohols often, undergo oxidation.
Stability totcard Halogens4 The behaviors of the three types of alcohols with halogens may be understood from a consideration of their structure: H
‘
Secondary
E>C-OH
Primary
H R-C-OH H
Tertiary
R-C-OH R\ R/
Since the first action of the halogen is to displace a hydrogen attached to a carbon atom, it is evident that the secondary alcohols will be the most reactive, because they contain a labile hydrogen attached to a carbon which is also linked to three groups (other than hydrogen). Next in order come the primary alcohols. But the tertiary alcohols are the most stable because no hydrogen is attached to the carbon of the C-OH group, and substitution can take place only in one of the R radicals. As regards the separate tertiary aIcohols, the one contain2 Noelting, Chimic & industrie, 6, 719 (1921); Schoetz, “Synthetlc Organic Compounds,” 123 (1926). a Be?., 47, 322 (1914). 4 Henry, Rec. tYav. chim., 26, 116 (1907).
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INDUSTRIAL A N D ENGi[NEERIXG CHEMISTRY
846
ing only CH3 groups (tertiary butanol) is the most stable. Kext in order come those with CH2 and with CH radicals, and the lability of the hydrogen in these is also affected by the nature of the attached groups. For instance, the alcohol CHa H
\
CH,>c CH~--IC-OH CHs/ is more reactive toward halogens than CHaCHEHz\
:3C-oH
The writers have frequently used solutions of bromine in tertiary butanol as a laboratory reagent where a watersoluble solvent is desired. They are quite stable even in sunlight, but decompose a t 80” to 90” C. Tertiary amylol is also comparatively stable to bromine, but the solution rapidly decolorizes at 80” C.
Behavior with Metals The stability of their 0-H bond is strikingly shown by the behavior of the tertiary alcohols with metals and metallic oxides. Metallic sodium reacts only slowly with tertiary butanol, even when they are refluxed together. Barium oxide, too, gives no alcoholate. Accordingly, tertiary butanol may safely be dehydrated by distillation from either of these substances. Tertiary amylol is pretty stable to sodium or barium oxide up to its boiling point, but if the temperature of the liquid, owing to the presence of higher boiling substances, rises much above 102” C. then interaction speeds up and a t 125” C. is fairly rapid. Neither sodium nor barium oxide can be used to dehydrate the hexyl and higher tertiary alcohols on account of the attendant decomposition which sometimes results in resins. These alcohols can, however, be obtained free from water by simple fractionation.
Behavior with Acid Chlorides Acetyl chloride reacts with tertiary butanol but, in contrast to its behavior with primary and secondary alcohols, yields tertiary butyl chloride and not the acetate. This result again shows the strength of the 0-H bond and the lability of the OH group. Norris and his co-workers6 have shown that, contrary to general belief, esterification of alcohols proceeds by the displacement, not of the hydroxyl group in the alcohols, but of the hydrogen atom in the hydroxyl, thus: 0
R CHz0
0 I
L--R-RcH~-o-cR
Primary alcohol
Acid
+H ~ O
Ester
They have shown by quantitative measurements that the ease of esterification in a series of alcohols depends upon the looseness of the bond holding the hydrogen to the oxygen. Now since the OH bond is very strong in tertiary butanol, the reaction with acetyl chloride takes another path and the labile OH group itself is displaced, yielding tertiary butyl chloride and acetic acid. 0 0 (CHs)a C OH
+ C1 CI/ CHs-h(CHs)s
C1
+ OH CII CHa
Properties of the Esters The methods which are ordinarily used to form organic acid esters of the primary alcohols do not yield the tertiary esters from the tertiary alcohols. Tertiary butyl acetate, a Private communication.
Vol. 18, N o . 8
a typical tertiary ester, is suitably prepared by the action of ketene with tertiary butanol. It is a liquid boiling a t 96’ C. with a somewhat fruity odor, but leaves a sharp aftereffect due probably to the fact that it hydrolyzes in the olefactory organs, liberating acetic acid, for it is readily hydrolyzed even by cold water. The hypochlorite estersb of the tertiary alcohols are of industrial importance. They are readily formed by the action of aqueous hypochlorous acid on the alcohols. Whereas the hypochlorite esters of the primary and secondary alcohols are very unstable and decompose explosively in bright light, the tertiary hypochlorite esters are quite stable. Tertiary butyl hypochlorite, for example, can be distilled without change, and if it is not exposed to bright light may be kept for months at ordinary temperatures with scarcely any decomposition. Like all the tertiary esters, it can be easily hydrolyzed by dilute alkaline solutions regenerating the alcohol. Physiological Effects
Few investigations have been made of the physiological effects of the aliphatic tertiary alcohols. It is known, however, that tertiary amylol (“amylene hydroxyl”) “is a safe, rapidly acting and occasionally useful but not analgesic hypnotic. ”’I An extension of our knowledge of the higher tertiary alcohols, including the unsaturated ones, may lead to results vital in its literal sense. Four Japanese workers8 have recently separated from cod-liver oil and from green foods a material which they regard as a definite cornpound,s with remarkable vitamin powers. It can actually be distilled a t 0.02 to 0.03 mm. pressure. When added to the food of the albino rat in the proportion of two parts per million of the ration by weight, i t will supply all the “Vitamin A” necessity for normal growth. This substance, which they have named “biosterin,” has the empirical formula C2iH2402. It contains three double bonds and the oxygen atoms are both in hydroxyl groups. One of these is held in the linkage of a primary or secondary alcohol and the other in that of a tertiary alcohol. A compound of 27 carbon, 44 hydrogen, and 2 oxygen atoms, to contain three double bonds, one primary or secondary alcohol group, and one tertiary alcohol groupthese are not specifications insuperable to the organic chemist. We may be on our way to the synthesis of such materials. And just as these workers on one side are endeavoring to learn the chemical structure of the active substances which they can separate from foods, so from the other side our knowledge must be built up about the effect of structure on the physiological properties in an homologous group. And when the two meet who knows but what we will be synthesizing vitamins in ton lots from petroleum? Chattaway and Backeberg, J . Chem. SOC. (London), 128,2999 (1923). U. S. Dispensatory, 20th ed. 8 Takahashi, Nakamiya, Kawakami, and Kilasato, Institute of Physical and Chemical Research, Scicnli$c Papers, 3, 81 (1925). 9 Many criticisms of the work of Takahashi and his colleagues art. contained in a paper by Drummond. Channon, and Coward, Blochem. J . , 1
7
19, 1097 (1925).
Distribution of Sulfur in Oil Shale In my paper under this title, THIS JOURNAL, 18, 731 (1926). the second sentence in the conclusion on page 733 should read: “The resinic sulfur found in those coals analyzed for resinic sulfur exists in quantities ranging from one-fourth t o all the organic sulfur.” E. P. HARDINC MINNEAPOLLS, MI“.
