Citral determination

According to Tiemann the following are the characters of a-citral and jS-citral, ljut as these were determined before the exact relationships of... 

The determination of citral in lemon-grass oil by the neutral sulphite absorption process ves results some 4 per cent, lower than those obtained by the bisulphite method, but the latter is that usually adopted in commerce, though, as alreadv stated, the former is official in the new Britiih Pharmacopmia. 

The condensation product is soluble, and it has been proposed to make-use of this reaction as an absorption process for the determination of citral in lemon oil, but owing to a very indistinct separation between the unabsorbed oil and the absorbing solution, it has been found practically impossible to get satisfactory results and tbe process has been abandoned in practice. 

IR spectroscopy of two supports was used for the determination of their surface acidity. The presence of Lewis acid sites on the surface of sepiolite allowed the preparation of a catalyst able to transform citral into menthol in fairly good yield under veiy mild conditions (90°C, 1 barH2). 

Determination of the acidic sites through IR spectroscopy of adsorbed CO is a valuable tool for the choice of the support when selective or multifunctional processes are to be set up. This technique allowed to identify a particular kind of silica as the support of choice for the selective hydrogenation of citral to citronellal and sepiolite as a Lewis acid support able to promote the one-step transformation of citral into menthol. 

The bed void fraction and the Reynolds number were determined with the experimental procedures reported in literature [7]. Inprehminaty experiments, citral hydrogenation was investigated in six parallel reactors under identical reaction conditions, i.e., at 25°C and 6.1 bar hydrogen with the residence time of 156 s. The... 

In preparation for scale-up of the strigol synthesis described by Sih (8), efforts were made to improve the yield of some of the seven steps involved in the scheme. Of these steps, nine are satisfactory from the standpoint of yield and experimental conditions. For three of the steps, we have improved the yield and/or experimental conditions such that the yield of (+ )-strigol would be raised to 2.85% overall from citral rather than 1.53% based on Sih s procedure and reported yields. Improvements were developed preparation of a-cyclocitral (III), the oxidation of the hydroxyaldehyde (V) to the ketoacid (VII), and for the preparation of the hydroxybutenolide (XVII). For the remaining five steps, our attempts to change experimental conditions have failed to improve, and in most cases to even obtain, the yields reported in the literature (8). We have considered the preparation of strigol analogs and determined the conditions and limitations for the preparation of a series of alkoxybutenolides (XVI) and a butenolide dimer (XVIII). Modification of the literature procedure (11) to eliminate the use of the mesylate (XX) and the use of polar aprotic solvents gave better yields of the 2-RAS (XXI). 

Kinetic experiments on the hydrogenation of prenal and citral were first carried out in the batch reactor with variation of aldehyde concentration, hydrogen partial pressure, ruthenium concentration and reaction temperature (Table 7). Stirring was provided at 2000 rpm in order to be sure that the overall reaction rate was determined by kinetics. 

Lemon peel oil is much more valuable than its juice therefore, extensive research efforts have been expended to determine its natural composition as a way to detect adulteration as well as to determine quality factors [6, 31, 32]. However, a few studies on lemon juice volatiles can be found [33-35]. Lemon oils are notable for possessing relatively low levels of limonene (more than 70%) and relatively high levels of a-pinene (1-2%), -pinene (6-13%), sabinene (1-2%) and y-terpinene (8-10%) [32]. The relatively high concentration of -pinene is thought to instil the green peely odour of lemon oil. The concentrations of aliphatic and monoterpenic aldehydes, (especially citral) as well as those of esters and alcohols are critical components in the perceived quality of the oil. As lemon oil is unstable, quality can deteriorate with improper storage, resulting in... 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

The determination of aldehydes and ketones is of importance in the analysis of those essential oils characterised especially by aldehydic or ketoruc principles, e g.,the citral contained in lemon and lemongrass oils, citronellal in citronella Oil and some eucalyptus oils, benzaldehyde in bitter almond oil, salicylaldehyde in meadow-sweet oil, anisaldehyde in aniseed and fennel oils, cuminaldehyde m cumin oil, cinnamaldehyde in cinnamon oil, carvone in caraway oil, pulegone in pennyroyal oil and methyl nonyl ketone in rue oil The determination of the aldehydes and ketones presents, however, difficulties and the above methods are moderately exact in only a few cases, especially when the content of aldehydes or ketones is considerable The bisulphite method is applicable particularly to the determination of cinnamaldehyde and benzaldehyde in cinnamon oil and bitter almond oil, and, up to a certain pomt, to that of citral in lemongrass Oil. The sulphite method gives good results in the same cases and for the determination of carvone and pulegone... 

This is extracted from the peel of the fruit of Citrus limomm by pressure, either manual or mechanical. 11 is a pale yellow, sometimes slightly greenish liquid with the smell of fresh lemons in time it resinifies, decolorises and acquires a special resinous odour. It consists mostly (about 90%) of limonene and contains also small proportions of other terpenes, citral (which determines its value, as it contributes largely to the aroma) and other aldehydes and traces of esters. 

Determination of the Citral.—Use is commonly made of Berth s method, based on the change of rotation due to removal of the aldehydes by means of alkali bisulphite. 

Other methods of determining citral (aldehydes) are that of Soldaim and Bertd and that of Romeo (Ann Lab Camera dt Commercio di Messina, 1908) Results obtained by Kleber s phenylhydrazine method or Walther and Bennet s hydroxylamine method are sometimes required m the trade, the latter gives lower results than other methods... 

Citral and citronellyl acetate, being powerful co-determinants of the odour. 

The same dilution technique is usually applied in the analysis of ethereal oils [210]. It can be used in the determination of aldehydes such as citral and citronellal in lemon oil (Oleum citri) and in Oleum verbenae, of anisaldehyde in Oleum anisi stellati. Oleum anisi and Oleum foeniculi, of cinnamaldehyde in Oleum cinnamomi, and of ketones, such as car-vone, in Oleum anethi, of pulegone and diosphenol. In all these cases, the oil is first diluted with ethanol and to this solution an aqueous solution of the supporting electrolyte is added, usually only 0.1 M LiCl. 

Oils of lemon and petitgrain citronnier, and oil of lime obtained by a mechanical process - Determination of citral (neral -i- geranial) content -Gas chromatographic method on capillary colnmns... 

The structure of isoxanthochymol has been revised [to reposition a prenyl double bond into a terminal position in keeping with the structure of xanthochymol reported last year (Vol. 8, p. 60)] despite an earlier (incomplete) report of an X-ray structure determination. Further details cf. Vol. 7, pp. 48, 49) of the chemistry and structures of (—)-bruceol (14 X = OH, Y = H), ( )-deoxy-bruceol, chromenes and citrans produced from phloroacetophenone and phloroglucinaldehyde by citral condensation, and rubranine have been published in a related paper the isolation of (—)-rubranine from Aniba rosaeodora... 

The physicochemical characteristics of these catalysts were determined and the behaviour of these catalysts was investigated in the hydrogenation of citral in terms of rate of hydrogenation and selectivity. 

If you enjoy solving puzzles, you might like to read through the two accounts of structural determination (myrcene and citral) below, without looking at the figures and work out the structures for yourself from the evidence as it unfolds. 

In a research directed toward monoacetalation of sucrose (26) by treatment with citral 27 (geranial and neral), widely used as chemical intermediates in the perfume industry [16], Queneau et al. [17] determined conditions for optimized acidic catalysis in dimethylformamide (DMF) which afforded good yields (>80%) of acetals 28 directly from the unprotected 26 in comparison with those obtained in a oil bath. With prolonged reaction times, cleavage to acetal 29 occurred (Scheme 12.11). 

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