Ricinoleic acid dehydration

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

Synthesis of CLA by Dehydration of Ricinoleic Acid (12-Hydroxy-c/s-9-Octadecadienoic Acid)... 

The most attractive method for production of pure 9,ll-c,t-CLA is through the dehydration of ricinoleic acid. Synthesis from this relatively inexpensive starting material has proven elusive as it is difficult to control the formation of dehydration products (124). Synthesis of 9,ll-c,t-CLA from ricinoleic acid has been reported (125), which, although an efficient reaction, uses expensive elimination reagents such as l,8-diazobicyclo-(5,4,0)-undecene. For most applications, the high cost of the elimination reagent increases the production cost beyond the level at which commercial production of CLA is economically viable. 

O 14 01%, CHjfCH ljCHO. Obtained by distilling castor oil under reduced pressure Rogers, J. dm. Ffiarm. dssoc., Sci Ed. 12, 503 (1923) Dominguez et at, J. Chem, Ed. 29, 446 (1952). Catalytic dehydration of ricinoleic acid methyl ester yields heptanal as a cleavage product in almost quantitative yield Panjutin, Chem. Zentr. 1928, II, 747. 

Dehydration of unsaturated alcohols is important only in special cases, since such starting materials are difficultly accessible. According to Scheiber,104 octadecadienoic acid can be prepared by dehydration of ricinoleic acid owing to its conjugated double bonds it is a valuable starting material for synthetic drying oils of tung oil type. 

Acidic dehydration of 1,4-diketo acids, as in the conversion of 9,12-dioxostearic acid to the 9,12-furanoid acid, effected with methanolic BF3 (10). 1,4-Diketones, made from ricinoleate, linoleate, or diynoic esters by Lie Ken lie and his colleagues (22-25), were converted to furanoid acids under acidic conditions (BF3 or toluenesulfonic acid). With 1,4-, 1,5-, and 1,6-diketones, ketocy-clopentenes and ketocyclohexenes were also obtained. Typical products ([7]-[9]) are formulated ... 

Dehydrated castor oil is made by thermal dehydration of the ricinoleic acid component of castor oil. Low-viscosity oils contain up to about 40% of conjugated 9,11-linoleic acid, together with 9,12-linoleic acid, polymerized acids and smaller amounts of less-unsaturated acids. 

Dehydration of a suitable precursor at high temperature under vacuo initially yielded a polyester (8), upon which pyrolysis afforded the trans-9,trans-11-18 2 isomer. For this procedure ricinoleic acid was first elaidinized, which means a transformation of the ds- double bond into a trans- double bond (9). The so formed ricinelaidic acid was then heated under vacuum at 235°C. Intermolecular esterification (estolide formation) yielded polyesters with a molecular weight of 1500 to 1600. Pyrolysis and simultaneous distillation furnished a crude product, which was recrystallized in 95% ethanol to furnish the desired trans-9,trans-W- % 2 isomer in a 35% yield. 

Ricinoleic acid rI-son-o- le-ik- [L ricinus + E oleic acid] (1848) n. Chief acid of castor oil, almost unique by reason of the presence of a hydroxyl group in the fatty acid chain. To exhibit drying properties, the ester must be dehydrated. Bp, 250°C per 15mmHg mp, 17°C Sp gr, 0.945. 

The dibasic acids, dimer acids, are produced commercially from vegetable oil fatty acids or esters, mainly C18 unsaturated fatty acids or esters, such as linoleic acid, ricinoleic acid, oleic acid. These fatty acids or esters derived from vegetable oils, such as dehydrated castor oil, tall oil, tung oil etc., are polymerized to give a mixture of dibasic and polybasic acids. This polymerized monomer chiefly includes dibasic dimeric fatty acids and small fractions of the monomeric, trimeric and higher polymeric fatty acids and, therefore, these are designated by the term dimer acids . These dimer acids find an outlet as important intermediates for the manufacture of plasticizers, synthetic lubricants, and high polymeric products because of their increased functionality compared with ordinary fatty acids. 

The main constituent of castor bean oil is ricinoleic acid (12-hydroxy-9-octade-cenoic acid). Around 1937, dehydrated castor oil appeared on the market in the United States as a substitute for tung oil. Ten years later the product was estabhshed as one of the most popular drying oils (1). It has been known since 1888 that castor oil could be dehydrated, and since 1914 it was known that the main isomers of linoleic acid formed had double bonds at positions 9,11 and 9,12, but the detailed composition of dehydrated ricinoleic acid was not investigated until recently. A German patent from 1930 (2) and a U.S. patent from 1934 (3) desaibe the preparation of dehydrated castor bean oils. A modified procedure was recently used to produce an 83% pure 9-cis,ll-trans CLA concentrate from purified ricinoleic acid (4). Main impurities were the 9-cis,li-cis and 9-c ,12-franx-octadecadienoic acids. Conventional dehydration... 

A concentrate with 83% 9-cis,ll-trans isomer was obtained from gentle dehydration of ricinoleic acid from castor bean oil and subsequent purification steps (4). The use of urea inclusion compounds does not seem to be a feasible procedure to separate 9-cis,l i-trans and l0-trans,l2-cis (23). Enzymes, however, are promising tools for these separations. A 98% concentrate of 9-cis,ll-trans was reported by using lipase from Geotrichum candidum. The enzyme was capable of esterifying selectively 9-cis, -trans to monohydric alcohols from a mixture of several isomers (24). A patent has been issued on purification and characterization of iso-merases from Propionibacterium acnes and Clostridium sporogenes. The purified isomerase preparations were able to quantitatively isomerize linoleic acid into the 10-trans,12-cis isomer of CLA (25). 

Ricinoleic acid contains a hydroxyl function at a stereogenic carbon atom. Such additional functional groups may interact with transition-metal catalysts causing directing effects or lead to their deactivation. In the hydroformylation of ethyl ricinoleate, the formed aldehydes are converted immediately into cyclic ethers by acetalization and subsequent dehydration (Scheme 6.87) [36]. 

Ricinoleic acid was polymerised via dehydration with an immobilised poly(e-caprolactone) (PCL) catalyst to give a polymer with MW up to 8,500 Da [14]. Immobilised CALB was efficient as a catalyst for the dehydration polycondensation of cis-9,10 epoxy-18-hydroxyoctadecanoic acid (from the outer birch bark) in toluene, in the presence of molecular sieves at 75 C, to give a polyester with the highest MW of 2.0 X lO Da after 68 h [15]. 

DCO n Nondrying castor oil which has been converted into a drying oil by the catalytic removal of water from its principal fatty acid (80% ricinoleic acid), forming approximately equal quantities with 9-11 and 9-12 unsaturation. The term DCO rather than dehydrated castor oil has been suggested and is being used for this... 

FIGURE 4.2 Biomaterials from castor oil. From top left castor oil ricinoleic acid ricinoleyl-sulfate lithium grease Oithium hydroxystearate) 10-undecylenic add ll-amino-undecanoic acid. From top right dehydrated castor oil sebadc add. 

R. is produced from - ricinoleic acid by - dehydration. The reaction is carried out at 200-320 °C without or with a catalyst (e.g., AI2O3). This goes together with an increase of the irons isomer content (- isomerism). The degree of conjugation can be increased. 

Most of the conjugated Cig acids are trienes but a diene 0tl2t 12%) is present in Chilopsis linearis seed oil along with some other less common acids. Conjugated octadecadienoic acids result from dehydration of ricinoleic and ricinelaidic acids (Section 1.9) and from alkali isomerization of linoleic acid. Claims have been made for the formation of the 8rt0, the four 9,11 and the four 10,12 dienes by one or both of these methods. 

The most convenient source of conjugated diene acids is via the dehydration of castor oil (Section 3.3.4) by heating ( 250°C) in the presence of an acidic catalyst. The product is complex and the dienes produced from ricinoleate are both conjugated (mainly A9,ll) and non-conjugated (mainly A9,12) in the proportion 1 3 or 4. Several configurational isomers are produced and double-bond migration complicates the product further. Alkaline isomerization of linoleic-rich oils also produces conjugated dienes (A9,ll and A10,12) but these processes have not proved to be of commercial value. 

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