Ursula Biermann

New Syntheses with Oils and Fats as Renewable Raw Materials for the Chemical Industry.

Oils and fats are the most important renewable raw materials for the chemical industry. Hitherto, industrial oleochemistry has concentrated predominantly on the carboxy functionality of fatty acids but, more recently, modern synthetic methods have been applied extensively to fatty compounds for the selective functionalization of the alkyl chain. Radical, electrophilic, nucleophilic, and pericyclic as well as transition metal catalyzed additions to the C-C double bond of, for example, oleic acid as the prototype of a readily accessible, unsaturated fatty acid have led to a large number of novel fatty compounds from which interesting properties are expected. Functionalization of C-H bonds in the alkyl chain is also feasible with remarkable selectivity. Effective and highly versatile catalysts for the metathesis of esters of unsaturated fatty acids have been developed, which lead to new and interesting omega-unsaturated fatty acids. The epoxidation of unsaturated fatty acids has been developed extensively. Enzymatic reactions allow syntheses with high selectivity and yield of mono- and diglycerides and esters of carbohydrates with a variety of surfactant properties. Regio- and enantioselective microbial hydrations and hydroxylations widen the spectrum of selective reactions. Of considerable significance is that, with the use of gene technology, natural oils and fats have been improved significantly and will be improved still further, insofar as they show a more uniform and often unusual fatty acid spectrum. Numerous fatty acids are now available in a purity which makes them attractive for synthesis and as raw materials for the chemical industry.

Oils and Fats as Renewable Raw Materials in Chemistry

Oils and fats of vegetable and animal origin have been the most important renewable feedstock of the chemical industry in the past and in the present. A tremendous geographical and feedstock shift of oleochemical production has taken place from North America and Europe to southeast Asia and from tallow to palm oil. It will be important to introduce and to cultivate more and new oil plants containing fatty acids with interesting and desired properties for chemical utilization while simultaneously increasing the agricultural biodiversity. The problem of the industrial utilization of food plant oils has become more urgent with the development of the global biodiesel production. The remarkable advances made during the last decade in organic synthesis, catalysis, and biotechnology using plant oils and the basic oleochemicals derived from them will be reported, including, for example, ω-functionalization of fatty acids containing internal double bonds, application of the olefin metathesis reaction, and de novo synthesis of fatty acids from abundantly available renewable carbon sources.

Neue Synthesen mit Ölen und Fetten als nachwachsende Rohstoffe für die chemische Industrie

Ole und Fette sind die wichtigsten nachwachsenden Rohstoffe der chemischen Industrie. Die industrielle Oleochemie konzentriert sich bisher uberwiegend auf die Carboxyfunktion der Fettsauren, doch wurden in letzter Zeit auch moderne Synthesemethoden zur selektiven Funktionalisierung in der Alkylkette auf Fettstoffe angewandt. Additionen an die C-C-Doppelbindung z. B. von Olsaure als Prototyp einer gut zuganglichen ungesattigten Fettsaure fuhrten zu einer Vielzahl neuartiger Fettstoffe mit interessanten Eigenschaften. Auch Funktionalisierungen von C-H-Bindungen in der Alkylkette sind bemerkenswert selektiv moglich. Es wurden effektive Katalysatoren fur die Metathese ungesattigter Fettsaureester entwickelt, die zu vielfaltig einsetzbaren ω-ungesattigten Fettsauren fuhrt. Die Epoxidierung ungesattigter Fettsauren wurde wesentlich weiterentwickelt. Enzymatische Reaktionen erlauben mit hoher Selektivitat und Ausbeute die Synthese von Mono- und Diglyceriden und von Kohlenhydratestern mit interessanten oberflachenaktiven Eigenschaften. Regio- und enantioselektive mikrobielle Hydratisierungen und Hydroxylierungen erweitern das Spektrum der selektiven Reaktionen. Die nativen Ole und Fette wurden durch Pflanzenzuchtung (auch gentechnisch) betrachtlich verbessert, und zahlreiche Fettsauren stehen heute in genugender Reinheit fur die Synthese und als Rohstoff fur die chemische Industrie zur Verfugung.

Friedel - Crafts Alkylation of Alkenes: Ethylaluminum Sesquichloride Induced Alkylations with Alkyl Chloroformates**

The formal addition of propane to nonactivated double bonds can be achieved with isopropyl chloroformate (2) in the presence of Et(3)Al(2)Cl(3). Thus, a 1:1 mixture of 10-isopropyloctadecanoic acid (3) and the 9-regioisomer is formed from oleic acid (1). The reaction may also be carried out with 1-alkenes by the addition of triethylsilane as a hydride donor.

Initiation of Radical Chain Reactions of Thiol Compounds and Alkenes without any Added Initiator: Thiol‐Catalyzed cis/trans Isomerization of Methyl Oleate

A kinetic study of the dodecanethiol-catalyzed cis/trans isomerization of methyl oleate (cis-2) without added initiator was performed by focusing on the initiation of the radical chain reaction. The reaction orders of the rate of isomerization were 2 and 0.5 for 1 and cis-2, respectively, and an overall kinetic isotope effect k(H)/k(D) of 2.8 was found. The initiation was shown to be a complex reaction. The electron-donor/-acceptor (EDA) complex of dodecanethiol (1) and cis-2 formed in a pre-equilibrium reacts with thiol 1 to give a stearyl and a sulfuranyl radical through molecule-assisted homolysis (MAH) of the sulfur-hydrogen bond. Fragmentation of the latter gives the thiyl radical, which catalyzes the cis/trans isomerization. A computational study of the EDA complex, MAH reaction, and the sulfuranyl radical calculated that the activation energy of the isomerization was in good agreement with the experimental result of E(A)=82 kJ  M(-1). Overall, the results may explain that the thermal generation of thiyl radicals without any initiator is responsible for many well-known thermally initiated addition reactions of thiol compounds to alkenes and their respective polymerizations and for the low shelf-life stability of cis-unsaturated thiol compounds and of mixtures of alkenes and thiol compounds.

Novel halo-oxo-allenic fatty ester derivatives from epoxidized methyl santalbate (methyl trans-11-octadecen-9-ynoate)

Methyl santalbate (methyl trans-11-octadecen-9-ynoate) from Sandal wood seed oil, Santalbum alum) was epoxidized to methyl trans-11,12-epoxy-octadec-9-ynoate (1). Treatment of compound 1 with tetrabutylammonium dihydrogentrifluoride, and boron trifluoride etherate gave the corresponding anti- (2a) (57%) and syn- (2b) (35%) fluorohydrin derivatives, respectively. These reactions were regio- and stereoselective in nature. The structures of the anti- and syn- isomers were confirmed by NMR spectroscopy. Ring opening of the epoxy system of compound 1 with lithium chloride gave the anti-chlorohydrin derivative (3) (89%). Oxidation of either compound 2a or 2b gave the same fluoro-keto acetylenic fatty ester (4) (75%), and compound 3 on chromic acid oxidation yielded the corresponding chloro-keto acetylene (5) (73%). Isomerization of compounds 4 and 5 with potassium carbonate in dichloromethane furnished the requisite fluoro-allenic (6) (63%, methyl 11-fluoro-12-oxo-9,10-octadecadienoate) and chloro-allenic (7) (80%, methyl 11-chloro-12-oxo-9,10-octadecadienoate) C(18) fatty esters. All products were confirmed by a combination of spectrometric and spectroscopic techniques.

Synthesis of Ethers by GaBr3-Catalyzed Reduction of Carboxylic Acid Esters and Lactones by Siloxanes

Ethers were synthesized by reduction of the respective esters catalyzed by gallium bromide (GaBr3 ) and using siloxanes, preferentially 1,1,3,3-tetramethyldisiloxane, as reductant. Methyl oleate, triglycerides, that is, tributyrine and glyceryl triundec-10-enoate as well as γ- and δ-lactones were converted into the respective ethers in high to moderate yields. γ-Lactones were reduced with high selectivity in the presence of a methyl ester functionality. The reduction has been carried out at room temperature or moderately elevated temperature of up to 60 °C using stoichiometric amounts of the reductant and 0.005-0.01 equiv of GaBr3 as catalyst per ester functionality without any solvent added. After a reaction time of 1-4 h the conversion of the substrate was 100 %. The product was separated from polymeric siloxanes formed as coupled product by simple distillation.

Regioselective Cationic 1,2‐ and 1,4‐Additions Forming Carbon−Carbon Bonds to Methyl Santalbate, a Conjugated Enyne

Lewis acid-induced carbocationic addition reactions to methyl santalbate [methyl (E)-octadec-11-en-9-ynoate] [(E)-1] give products by regioselective formation of a new carbon−carbon bond at C-9 of the molecule chain. The allenic fatty acid derivatives methyl 12-chloro-9-(1-oxoheptyl)-9,10-octadecadienoate (2) and methyl 9-isopropyl-9,10-octadecadienoate (3) were obtained by Friedel−Crafts acylation of 1 with heptanoyl chloride and alkylation of 1 with isopropyl chloroformate, respectively. While the reaction between 1 and formaldehyde induced by Me2AlCl or Et3Al2Cl3 gives a mixture of the conjugated chlorodienes 5a and 5b, the corresponding reaction carried out in the presence of AlCl3 affords the α,β-unsaturated ketone 6.

Friedel‐Crafts‐Alkylierung von Alkenen: Ethylaluminiumsesquichlorid‐induzierte Alkylierungen mit Chlorameisensäurealkylestern

Die formale Addition von Propan an nichtaktivierte Doppelbindungen gelingt mit Chlorameisensaureisopropylester 2 in Gegenwart von Et3Al2Cl3. So entsteht aus Olsaure 1 ein 1:1-Gemisch aus 10-Isopropyloctadecansaure 3 und dem 9-Regioisomer. Die Reaktion last sich auch mit 1-Alkenen unter Zusatz von Triethylsilan als Hydriddonor durchfuhren.

Some carbon, nitrogen‐ and carbon, oxygen‐bond forming additions to unsaturated fatty compounds

Unsaturated fatty compounds 1–7 were functionalized by ionic and free radical C,N- and C,O-bond forming additions to the C,C-double bond. C,N-bond forming additions of nitriles (Ritter reaction), iodine isocyanate, iodine azide, nitrogen oxides, nitrosyl chloride, N,N-dichlorourethane and azide as well as C,O-bond forming additions of alcohols and carboxylic acids are reviewed. Einige Additionen an ungesattigte Fettstoffe unter Ausbildung von C,N- und C,O-Bindungen Ungesattigte Fettstoffe 1–7 wurden durch ionische und radikalische Additionen an die C,C-Doppelbindung funktionalisiert. Uber Additionen von Nitrilen (Ritter-Reaktion), Iodisocyanat, Iodazid, Stickoxiden, Nitrosylchlorid, N,N-Dichlorurethan und Azid unter Ausbildung einer C,N-Bindung und von Alkoholen und Carbonsauren unter Ausbildung einer C,O-Bindung wird zusammenfassend berichtet.