direct oxidation may be adapted to use impure ethylene, the operators prefer to charge 97 to 9 8 % ethylene with no trace of acetylene in it. The reactor with its specially prepared silver catalyst is responsible for most of the capital cost in the direct oxidation. Since the complete oxidation of ethylene to carbon dioxide and water releases about 10 times as m u c h heat as the de sired reaction, it is obvious that every effort must be made to operate at the highest possible yield. Even with 5 0 % yield ( which is typical of commercial installations) the desired reaction liberates only 8% of the total heat evolved. There fore, a very efficient cooler with many tubes must b e provided to prevent local overheating in the catalyst bed. An interesting approach to the prob lem of excessive carbon dioxide produc tion is the discovery by Law that a small amount of an anticatalyst, such as ethyl ene dichloride, will suppress the undesir able side reaction to some extent. At present the chlorohydrin process seems to hold an economic advantage, but there are several factors which may alter the relationship. For instance, the following situations tend to make the direct oxidation method more desirable: ( 1 ) An increasing volume of ethylene oxide is being converted to chemicals other than glycol, particularly to acrylonitrile by reaction with hydrogen cy anide. ( 2 ) Decreasing construction costs will result in lower charges for deprecia tion and maintenance. ( 3 ) A considerable amount of research is being directed toward improving the yields of the oxidation. Oxidation of Light Hydrocarbons. The history of the oxidation of L P G (liquid petroleum gas) hydrocarbons dates back to the late 1920's when Hanlon-Buchanan Corrp. (absorbed into Warren Petro leum Corp. in 1946) became interested in the development of the process for the utilization of propane and butane, at that time waste products of the natural
gasoline industry. In the early days this industry had no facilities for stabilizing the natural gasoline. ' T h e high-vapor pressure gasoline was pumped into open tanks and allowed to "weather d o w n " until it h a d reached the preferred vapor pressure. The vapors from this process contained largely propane and b u t a n e and were lost to the atmosphere. In order possibly to utilize this vast quantity of propane a n d b u t a n e Hanlon-Buchanan in stalled a pilot plant at Iowa State College under the direction of O. R. Sweeney, for t h e purpose of developing a process for conversion of L P G hydrocarbons into oxygenated chemicals by direct oxidation with air. The data obtained at Ames were encouraging to t h e extent that HanlonBuchanan decided to construct a semicommercial plant at Good H o p e , La., w h e r e thousands of gallons of oxidized product were produced. This plant was eventually abandoned in 1933 for t h e following reasons : ( 1 ) Other outlets for propane and b u t a n e were being dis covered; ( 2 ) market conditions at t h e time would not support a plant producing chemicals of this type, such as acelaldehyde, formaldehyde, acetic acid, methyl alcohol, and ethyl alcohol; and ( 3 ) tech nology had not been developed to t h e point where the oxidation products could be separated into its individual compo nents—in other words, commercial grade chemicals. Shortly after the last war, a similar process was commercialized at Bishop, Tex., by Celanese Corp. Much work has been done on t h e gen eral subject of oxidation of L P G hydro carbons, as evidenced by the m a n y issued patents and magazine articles published on the process. T h e process may employ a catalyst or it may be noncatalytic. Cities Service Oil Co. at Tallant, Okla., in a partial oxidation plant developed a process for the reaction of oxygen con taining gases with natural gas at elevated temperatures and pressures in the presence of a catalyst. Practically all of t h e typi
cal oxidation catalysts were claimed as beneficial, and it has been stated t h a t aluminum phosphate is now being em ployed. In general, partial oxidation processes utilizing propane and butane give a com plex reaction mixture. This tends to make it extremely difficult to purify t h e com ponents, in m u c h the same fashion as in the Fischer-Tropsch synthesis. This is evidenced b y t h e fact that even today some of the chemicals produced by this method are not of sufficient purity for certain purposes. A typical oxidation re action product contains such chemicals as acetaldehyde, methyl formate, methylal, propionaldehyde, acrolein, acetone, di methyl acetal, tetrahydrofuran, methanol, ethanol, isopropanol, n-propanol, methyl ethyl ketone, acetal, formaldehyde, formic acid, butyl alcohol, dioxolanes, ethylene and propylene glycols, and many others. Therefore, in order to separate these chemicals it is necessary to resort to such tools as simple fractionation, azeotropic distillation, extractive distillation, adsorp tion, absorption, solvent extraction, a n d evaporation. Chemicals can be p r o d u c e d so cheaply by the partial oxidation of L P G hydro carbons that it will not be surprising to see them displace, more a n d more, the same chemicals manufactured by other methods. T h e r e are many other processes by which the petroleum companies can enter the chemical field. A few of t h e processes involve detergents, chlorinated hydrocar bons, carbon disulfide, thiophene, mercaptans, nitroparaffins, and ammonia. Acknowledgment T h e author wishes to acknowledge the helpful assistance given b y J. H. McCracken and J. T. McDonnell of Warren Petroleum Corp. in t h e preparation of this paper. PRESENTED at the Fifth Annual Southwest Re gional Meeting of the AMERICAN CHEMICAL SOCIETY, Oklahoma City, Okla., Dec. 8-10, 1949.
Note on the Naming of Geometric Isomers Of Polyalkyi Monocycloalkanes MORTON B. EPSTEIN and FREDERICK D. ROSSINI National Bureau of Standards, Washington, D. G HERE exists T. method for the
no generally accepted systematic designation of geometric isomerism among the polyalkyi monocycloalkanes. (For examples of methods that have been used, see Egloff, "Physical Constants of Hydrocarbons, Vol. II, Cyclanes, Cyclenes, Cyclynes, and other Alicylic Hydrocarbons, " Reinhold Publishing Co., New York, Ν . Υ., 1940.) Among the dialkyl monocycloalkanes, geo
1910
metric isomerism usually has been desig nated by a single prefix, cis or tram, the former indicating that the t w o alkyl groups are on t h e same side of the ring, assumed plane, and the latter indicating that the alkyl groups are on opposite sides of the ring. An example of this m e t h o d of naming is cis-1-methy 1-3-ethylcyclopentane. Among the trimethyl monocyclc "Hcanes,
CHEMICAL
geometric isomerism usually has been in dicated by a set of prefixes, cis or trans, placed together at the beginning of the name. These prefixes designate whether the alkyl groups are on the same side or on opposite sides of the ring, assumed plane, as an arbitrarily selected side of the ring ( o r its equivalent, an arbitrarily selected point in s p a c e ) . This arbitrary side ( or point ) customarily has been
AND
ENGINEERING
NEWS
CH, CH,
( a ) l,frarw-2,c/s-3,/rans-4-tetramethylcyclopentane
l·/
H.,C H.,C
CH3
CH, CH, C2H»
( b ) l-methyl-ras-3-ethyl-/raTW-5-propylcyclohexane l-methyl-ras-3-ethyl-/rarw-5-propylcyclohexane or, with the substituents in alphabetical order, 1-ethyle«-3-methyl-traris-5-propylcyclohexane
H H C C
CH, CH, (c)
l,6^-2,irûn^-3-trimethyl-irûrw-l-ethylcyclopentane
or
with the substituents in alphabetical order, 1-ethylfrûrw-l,trûns-2,ds-3-trimethylcyclopentane frflrw-l,trûris-2,ds-3-trimethylcyclopentane
JJ 3 C x
CH3 (d)
l,cis-2jran#-$,cis-4,tram-5-pentmethy\-trans-6-ethy\l,c/6-2,/rfln^-3,ct5-4,ir«rw-5-pentmethyl-irflrLS'-6-ethyl- H3C y cyclohexane or, with the substituents in alphabetical order, l-ethy\-cis-2,trans-3,cis-4:,trans-5,trans-6-penta.methylcyclohexane CJk
^\CHa
V O L U M E
2 8,
NO.
23
»
»
CH*
( c ) i n F i g . 1 illustrate this method of naming. It should be noted that t h e proposal is restricted t o consideration of geometric isomerism. Selection of a name involves also t h e related problems of numbering t h e ring a n d of ordering the substituents. These problems, however, should be treated separately, as they involve additional classes of compounds, for example, t h e alkyl benzenes. Similarly, separate conventions should be adopted for the designation of optical isomerism. Special cases of n u m b e r i n g do exist which are peculiar t o the alkyl monocycloalkanes. T o cover these, t h e sentence regarding t h e precedence of cis over trans has been a d d e d . An illustration of this is given in ( d ) of Fig. 1. Where t w o different alkyl groups are attached t o t h e same carbon atom of the ring ( quaternary carbon atom ), i t is suggested that in t h e interest of clarity an orientational prefix be assigned to each alkyl group, as in example ( c ) i n F i g . 1. W h e r e t h e groups attached t o t h e quarternary carbon atom a r e identical, i t is suggested t h a t t h e use of r e d u n d a n t p r e fixes b e a v o i d e d , as in 1,1-dimethylcyclopentane. W i t h regard t o punctuation, it is t o be noted that the n a m e is written exactly as it would b e in t h e absence of the prefixes cis a n d trans, a n d t h e n "cis-" or "trans-" is inserted at each appropriate place. Thus, 1,2,3-trimethylcyclopentane would become 1 -cte-2,cw-3-trimethylcyclopentane or l,ci$-2,rrara-3-trimethylcyclopentane or l,iran5-2,cis-3-trimethylcyclopentane. In addition t o meeting t h e objections
» ·
JUNE
5,
1950
Punctuation T h e matter of p u n c t u a t i o n w a s not stressed in the previously p u b l i s h e d note on t h e naming of ci*s a n d trans isomers of hydrocarbons c o n t a i n i n g olefin double bonds, M. B . E p s t e i n a n d F . D . Rossini, C H E M . E N G . NEAVS, 2 6 , 2 9 5 9 ( 1 9 4 8 ) .
Fig. 1 selected so that the first alkyl group n a m e d will be designated cis. A n example of this is the following: c/s,CM,rr«n.s-l,2,4-trimethylcyclopentane. From the standpoint of systematic enumeration and indexing, it is necessary t h a t there b e available a method w h i c h c a n be extended t o t h e naming of all alkyl monocycloalkanes. There are, however, t h e following objections t o t h e methods outlined above: ( a ) T h e m e t h o d applied to t h e dialkyl compounds cannot be extended in a simple a n d satisfactory w a y to triaikyl, tetraalkyl, and polyalkyl compounds generally; ( b ) regarding t h e second method, t h e r e a r e no established conventions for i t s p r o p e r application even to certain simple triaikyl cycloalkanes, as, for example* t h e 1,3-dimethyl-l-ethylcyclopentanes. W h e n applied to highly substituted cycloalkanes,. t h e m e t h o d is a p t to become needlessly cumbersome. Substantially all of these difficulties c a n b e eliminated by t h e following suggested method. Geometric isomerism among cycloalkanes having t w o or more alkyl substituents is designated b y referring t o t h e first substituent named t h e geometric configuration of the remaining groups. T h e prefix cis or trans is applied to a given .group according t o whether it is o n t h e same side or on t h e opposite side of t h e ring (assumed p l a n e ) a s the first n a m e d or reference group. In each instance, t h e prefix is to b e placed immediately before t h e number locating the attachment of t h e given alkyl group. W h e r e choice of n a m e s exists, cis will be preferred to trans, for lowest numbers. Examples ( a ) , ( b ) , a n d
outlined in the first p a r a g r a p h , t h e recommended m e t h o d lias t h e a d d e d a d v a n tages of providing rapidly a clear image of the structure of the molecule, of not requiring the c h a n g i n g of cis names to trans names (or vice versai) for c o m p o u n d s already named a c c o r d i n g to t h e present methods, a n d o f p e r m i t t i n g t h e systematic naming of a l l geometric isomers of the alkyl monocycloalkanes. I n essence, the method unifies t h e n o m e n c l a t u r e designating geometric isomers of alkyl monocycloalkanes with t h e n o m e n c l a t u r e recently proposed for t h e g e o m e t r i c isomers of olefins, diolefins, e t c . Finally, through associating a given prefix directly with t h e group to which it refers, this m e t h o d is patterned after the accepted convention of associating directly with a given group the numeral locating its point of attachment.
The
punctuation in t h e c a s e of t h e olefin hydrocarbons is t h e s a m e as above, namely, the name is w r i t t e n exactly as it would be in t h e a b s e n c e o f t h e prefixes cis and trans, and t h e n "eus-" or "trans-" is inserted at each a p p r o p r i a t e place. Thus, one would write 1,3-pentadiene, which would become l,c£s-3-pentadiene or 1, trarw-3-pentadiene. In t h e n o t e o n the naming of the cis and trans isomers of hydrocarbons c o n t a i n i n g olefin double bonds, cited above, two errors in p u n c tuation inadvertently occurred a n d should be corrected a s follows: E x a m p l e ( 4 ) should be w r i t t e n 2-methyl-l,frarw-3-pentadiene; E x a m p l e ( 5 ) should b e written 3-ferf-butyl-ci5-2,c/5-4-hexadiene. T h e method is d e s i g n e d t o cover the naming of g e o m e t r i c isomers only. However, each geometric isomer is either inactive or resolvable into t w o optical isomers, in w h i c h ca.se t h e isomers m a y be designated as d ox I, representing the dextro and laevo rotatory molecules, respectively. T h u s , t h e t w o optical isomers of example ( d ) in F i g . 1 could b e named d- a n d Z-l,cis-2,£rarw-3,cw-4,£nzns-5-pentamethyl-ifûn^-6-ethylcyclohexane. C. D. H u r d has p o i n t e d o u t t h a t t h e r e m a y be used a n alternative method based upon the stereochemistry of t h e sugars, in which the trivial n a m e s of the sugars are used. T h e foregoing m e t h o d will b e used in the systematic n a m i n g of hydrocarbons in the tables of t h e American Petroleum Institute Research Project 44. I t is hoped that other laboratories dealing with alkyl cycloalkanes will also a d o p t this method of naming s u c h compounds. Grateful acknowledgment is m a d e to L. Schmerling, E . J- Crane, H . S. Nutting, C. D. Hurd, Α. ΊΜ. Patterson, K. W. Greenlee, a n d M a r y Alexander for their constructive comments a n d criticism. T H I S w o r k w a s p e r f o r m e d a s p a r t of t h e A m e r i c a n Fetroleum I n s t i t u t e Research Project 4 4 o n the C o l l e c t i o n , A n a l y s i s , a n d C a l c u l a t i o n of D a t a on the P r o p e r t i e s of H y d r o c a r b o n s .
1911
