Boron Adds to Halogenated Vinyl Carbon a-Haloorganoboranes rearrange through transfer reactions without carbene formation 150TH
ACS
NATIONAL
MEETING
Organic Chemistry When a borane adds to the double bond of a vinyl halide, 60 to 95(/c of the boron is introdueed at the halogenated carbon in the systems studied by Dr. Daniel |. Pasto and his coworkers, Sister Riceila Snyder and Dr. Padma Balasubramaniyan, at the University of Notre Dame. By studying the chemistry of alphaand beta-substituted organoboranes, Dr. Pasto found that alpha-substituted organoboranes undergo alpha-transfer rearrangements when the substituent is halogen, oxygen, or sulfur. Betasubstituted organoboranes undergo either beta-transfer or elimination. Dr. Herbert C. Brown of Purdue University, who developed hydroboration as a synthetic technique, had pre-
dicted that vinyl halides ought to add borane in both possible directions. Dr. Pasto has gone on to show that the major intermediate, an Q:-haloorganoborane, rearranges through transfer reactions and does not produce free carbenes. Dr. Brown had suggested that a-haloorganoboranes would be ideal systems for carbene formation. Elimination reactions form olefins which may undergo further hydroboration in either direction to give other organoborane derivatives. This makes it difficult t® distinguish between simple transfer reactions and the elimination-readdition sequence. However, Dr. Pasto distinguished between the two processes by choosing starting materials in which the directive effect of the substituent would act in a direction opposite to readdition to the olefin formed by elimination. He used a remote group to follow the direction of addition.
CARBENES. Dr. Daniel Pasto, Sr. Riceila Snyder, and Dr. Padma Balasubramaniyan (left to right) discuss data from studies of organoborane reactions. The Notre Dame chemists have shown that a-haloboranes do not produce free carbenes 54
C&EN
SEPT.
2 0,
1965
Hydroboration of /?-bromostyrene, followed by hydrolysis and oxidation, gave /J-phenylethyl alcohol as the only alcoholic product. The lack of a-phenylethyl alcohol, which would have arisen through an elimination-readdition sequence, indicates that at least 95% of the boron was introduced at the carbon bearing the bromine. Hydroboration of 4-fcrf-butyl-lchlorocyclohexane gives a mixture of /erf-butylcyclohexanols (80r,< cis- and frtf/is-4-fCTf-butylcyclohexanols and 20(/c cis- and f/Y//i.s'-3-f erf-butylcyclohexanols). The 3-ferf-butyl-cyclohexanols, and a comparable amount (20',r ) of the C-4 isomers, are formed by the hydroboration of 4-fcrf-butylcyclohexene which, in turn, is formed by a solvent (tetra.hydrofuran) catalyzed trans elimination of the /^-chloroorganoborane. (This elimination does not occur in diethyl ether.) The remaining boron (60'v) must have added to the chlorine-bearing carbon. To detect the possible formation of carbenes (which would tend to insert intramoleeularly or rearrange to olefins), chlorocycloheptene and the 2chloro- and 2-bromo-2-butenes were hydroborated. No products were formed which could have arisen from carbene intermediates. However, a carbene might have formed and inserted into a boron-hydrogen bond before rearrangement or intramolecular insertion could occur. To investigate this possibility, Dr. Pasto hydroborated /3-bromostyrene with phenylthioborane (more than 80'< of the boron was introduced at the carbon bearing the bromine). Dr. Pasto found that 4(Y-f of the products were formed through a rearranged intermediate bearing the phenylthio group on the carbon which formerly bore the halogen. Since a carbene would not have inserted into the boronsulfur bond, this is further evidence against carbene formation. The Notre Dame group also studied the stereochemistry of elimination reactions involving /^-substituted organoboranes. Substituted styrenes of known stereochemistry were deuteroborated and the stereochemistry of the resulting deuterostyrene was determined by nuclear magnetic resonance spectroscopy. /3-Ethoxyorganoboranes undergo a spontaneous cis elimination, but /J-thio-derivatives do not spontaneously eliminate. In cyclic systems, ^-halo-derivatives undergo a spontaneous trans elimination in tetrahydrofuran.
TO SERVE THE CHEMICAL WORLD BETTER WITH WATERSOLUBLE POLYMERS
BESSERE C M W I I S C H I ERZEUGWSSE DURCH WASSERLOSLICHE POlYMERE
POUR POUVOIR MIEUX SERVIR L'INDUSTRIE CHIMIQUE AU MOYEN DES POLYMERES SOLUBLES A L'EAU
With the recent completion of its water-soluble cellulosics plant at Zwijndrecht, The Netherlands, Hercules can now meet increasing demand from European industry for Natrosol* nonionic hydroxyethyl cellulose with a European source of supply. The plant is also capable of making purified CMC, anionic sodium carboxymethylcel· lu l'ose, which is widely used in many industries. Both types of Hercules* water-soluble polymers, also made at Hopewell, Virginia, U.S.A., are widely employed throughout the world as thickeners, protective colloids, binders, stabilizers, emulsifiers, filmformers, and suspending agents.
Die kurziich erfolgte Fertigstellung des Werkes fur wasserlosliche Ceflulosederivate in Zwijndrecht, Holland, ermogiicht Hercules die wachsende Nachfrage der europaischen Industrie nach Natrosol*—eine nichtionogene Hydroxyathylcellulose—• aus europaischer Produktion zu decken. Das Werk ist auch darauf eingerichtet, veredelte CMC— anionaktive Natriumcarboxymethyicellulose—herzustellen, tile in vielen Industrien Verwendung findet. Beide Arten wasserloslicher Polymere, die auch in Hopewell, Virginia, USA, hergestelltwerden, sind in alien Teilen der Welt als Verdicker, Schutzkolloide, Binde-, Stabilisierungs-, Emulgier- und Aufschlammungsmittel sowie als Filmbildner geschatzt.
Grace a l'etablissement recent d'une usine pour la production de matieres cellulosiques solubles a Peau, a Zwijndrecht (Pays-Bas), la Societe Hercules est en position de faire face a la demande croissante de Pindustrie europeenne pour le Natrosol*-hydroxyethylcellulose, produit nonionique-, maintenant fourni par une source europeenne. Cette usine est egalement equipee pour la production de CMC purifiee -carboxymethylcellulose de sodium, produit anionique- qui est employee a tres grande echelle dans de nombreuses industries. Les deux sortes de polymeres solubles a Peau, egalement fabriques par Hercules a Hopewell (Virginie) Etats-Unis, sont couramment employes dans le monde entier en tant qu'agent epaississant, colloide protecteur, liant, stabilisant, emulsifiant, filmogene et agent de suspension.
*HERCULESTRADEMARK
V.'ARENZCICHCN
* MARQUE
For details of Hercules water-soluble polymers, write: N.V. H E R C U L E S POWDER COMPANY P.O. Box 6189, The Hague, Netherlands
H E R C U L E S P O W P E R COMPANY INCORPORATED
Wilmington, Delaware 19899
H E R C U L E S POWDER COMPANY LIMITED One Great Cumberland Place, London, W . l . England 055-1
Gas Chromatography Separates Sugars Single-phase column packing permits quantitative analysis with GC techniques 150TH
ACS
NATIONAL
MEETING
Carbohydrate Chemistry
Scientists at the U.S. Department of Agriculture have developed a simple, quantitative method for analyzing sugar mixtures. Using gas-liquid chromatography, Dr. J. S. Sawardeker and co-workers at the Northern Regional Research Laboratory, Peoria, 111., have been able to separate 10 alditol acetates and to apply the method to analyzing monosaccharides. The simple method will greatly facilitate the study of carbohydrates, Dr. Sawardeker says. The most reliable quantitative methods now depend on separating a mixture by column or paper chromatography, and analyzing each component. Although gas-liquid chromatography is a logical alternative to these time-consuming methods, the problem of completely resolving mixtures of sugars has remained because, in converting the free sugars to volatile derivatives, they isomerize. A mixture of glucose, galactose, and mannose, for example, gives at least seven major peaks when converted to derivatives and chroma-
tographed. Thus, GLC has had limited use for the quantitative separation of sugar mixtures. One way out of the dilemma is to reduce the free sugars to their alditols, which cannot isomerize, and to convert these to the volatile acetates for analysis by gas chromatography. This technique was reported in 1961 by Dr. S. W. Gunner, Dr. J. K. N. Jones, and Dr. M. B. Perry. Their method suffered from two major drawbacks, Dr. Sawardeker says. It couldn't completely resolve alditol mixtures, such as galactitol and glucitol. And the method required a complex, three-phase column that was difficult to reproduce. At USDA, Dr. Sawardeker, Dr. J. H. Sloneker, and Dr. Allene Jeanes used the same basic approach. Their column packing, however, contains a single liquid phase, making the method easily reproducible, and thus adaptable for routine analyses. The packing, commercially available from Applied Science Laboratories, State College, Pa., is Gas Chrom Q precoated with 3 % ECNSS-M (an organosilicone polyester of ethylene glycol succinate and a cyanoethyl-type silicone).
The USDA workers reduced the sugar mixture to the alditols with sodium borohydride and converted these to their completely acetylated derivatives with acetic anhydride and pyridine. They cooled the solution and injected it directly into the gas chromatograph. Using a column made of 10 feet of copper tubing, 0.25-inch o.d., they were able to separate quantitatively the acetates of these 10 alditols from a single mixture: glycerol, erythritol, L-rhamnitrol, L-fucitol, ribitol, L-arabinitol, xylitol, D-mannitol, galactitol, and D-glucitol. There was no evidence of any decomposition or of any other thermally induced change, Dr. Sawardeker reports. The analysis can be completed within 80 minutes at a column temperature of 190° C. The data show an accuracy of ± 2 % based on the monosaccharides present in the original mixture. Dr. Sawardeker's group tried three other liquid phases for the GLC column. Carbowax 20M severely retarded the alditol acetates, they found, and the compounds could not be eluted without degradation. A phase made by esterifying the terminal hydroxy Is of Carbowax 20M with terephthalic acid worked much better. It separated all the alditol acetates, except galactitol acetate, from glucitol acetate. A column containing XE-60 did not resolve the acetates of ribitol and arabinitol and those of rhamnitol and fucitol.
Improved Column Packing Resolves Ten Components
c o
Sensitivity: Range 100, attn. 8X Column temperature: 190° C. Detector temperature: 270° C. Injection port temperature: 300° C. Helium flow rate: 60 ml./minute Sample size: 4 n\. of 1 % solution
20
10
30
40 Time/minutes
50
60
1 2 3 4 5 6 7 8 9 10
70
This gas chromotogram of alditol acetates was obtained on a ten-foot column containing 3% ECNSS-M. By reducing sugars to alditols, isomerization is prevented and separate peaks are obtained for each component. 56
C&EN
SEPT.
2 0,
1965
Glycerol Erythritol L-Rhamnitol L-Fucitol Ribitol L-Arabinitol Xylitol D-Mannitol Galactitol D-Glucitol
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