Ester volatiles, production

Reflux Distillation Unit. The apparatus shown in Fig. 38 is a specially designed distillation-unit that can be used for boiling liquids under reflux, followed by distillation. The unit consists of a vertical water-condenser A, the top of which is fused to the side-arm condenser B. The flask C is attached by a cork to A. This apparatus is particularly suitable for the hydrolysis of esters (p. 99) and anilides (p. 109), on a small scale. For example an ester is heated under reflux with sodium hydroxide solution while water is passed through the vertical condenser water is then run out of the vertical condenser and passed through the inclined condenser. The rate of heating is increased and any volatile product will then distil over. 

Obviously, the use of a nonvolatile ionic liquid simplifies the distillative workup of volatile products, especially in comparison with the use of low-boiling solvents, where it may save the distillation of the solvent during product isolation. Moreover, common problems related to the formation of azeotropic mixtures of the volatile solvents and the product/by-products formed are avoided by use of a nonvolatile ionic liquid. In the Rh-catalyzed hydroformylation of 3-pentenoic acid methyl ester it was even found that the addition of ionic liquid was able to stabilize the homogeneous catalyst during the thermal stress of product distillation (Figure 5.2-1) [21]. This option may be especially attractive technically, due to the fact that the stabilizing effects could already be observed even with quite small amounts of added ionic liquid. 

In some cases we may benefit from adopting a semi-continuous mode of operation, e.g. to a batch of one reactant we continuously feed the other reactant, while removing a volatile product continuously. An example where this is advantageous is the production of ethyl-4-pentenoate, CH2=(CH2)3(CO)OEt from allyl alcohol and triethyl orthoacetate, CHs-CfOEt). Continuous addition of allyl alcohol to a batch of triethyl orthoacetate and continuous removal of the produced ethylalcohol (and. some allyl alcohol) by distillation resulted in high yields of the dersired ester ethyl-4-pentenoate. By contrast, if allyl alcohol and triethyl orthoacetate were reacted in a batch-wise manner the product consisted of a 1 1 mixture of the desired ester and the undesired ester (Anderson, 2000, p 279 Bollyn and Wright, 1998). 

The lipase-catalyzed fatty acid ester hydrolysis and the lipoxygenation of free polyunsaturated fatty acids are involved in the same lipid degradation pathway. They are respectively the first and second reaction in the lipoxygenase pathway (Fig. 3) [87-91]. The pathway produces volatile products of considerable importance in food technology including Cg[92, 93] or Cg- 94—96 aldehydes and alcohols from polyunsaturated fatty... 

A mixture of triphenyl phosphite (0.1 mol), aldehyde (0.15 mol), ZNH2 (0.1 mol), and glacial AcOH (15 mL) was stirred for ca. 1 h until the exothermic reaction subsided. The mixture was heated at 80-85 °C for 1 h and volatile products were removed in vacuo. The oily residue was dissolved in MeOH (180 mL) and left for crystallization at —10 °C. After 1-3 h, the crystalline ester was collected by filtration and recrystallized by dissolution in the minimum amount of hot CHC13 (30-40 mL) and addition of a fourfold volume of MeOH. 

To a soln of 2-methylprop-l-ene in CH2C12 (5 mL, prepared by sparging with 2-methylprop-l-ene for 10 min) was added TMSBr (87 xL, 0.66 mmol). After 5 min, a soln of the phosphonate methyl ester 78 (100 mg, 0.13 mmol) in CH2C12 (lmL) was added to the TMSBr soln and the reaction flask was sealed with a septum. After stirring at rt for 24 h, the flask was carefully vented with a small bore needle to release excess pressure. The solvent and volatile products were removed in vacuo and the residue was reevaporated twice from CHC1> MeOH (4mL) was added, and the white solid that formed was collected and dried in vacuo to yield 79 yield 63 mg (64%) mp 225-227 °C 31P NMR (DMSO-rf , 6) 24.49. 

In order to expand the worldwide market, considerable efforts are being devoted to improve the image of Madeira wine. Consequently, their characteristics have to be well defined. So, in order to define and describe the particular characteristics and the authenticity of the product, secondary metabolites of grape and wines mainly linked to a specific variety, must be deeply studied. In Madeira wine, these compounds are mainly included in the chemical classes of mono and sesquiterpenoids C13 norisoprenoid higher alcohols, ethyl esters, volatile fatty acids, carbonyl compounds, sulfur compounds, furanic compounds, lactones, and polyphenols. 

They assumed that the primary cation radical of PMMA spontaneously and quickly dissociated to form carbocation, which then recombined with the liberated electron to form an excited radical with a ferr-alkyl structure. This excited radical was thought to be the precursor of the scission of the main chain. This reaction model interpreted well their observation that the G value for the scission of the side chain was close to that of the main chain and that the mercaptan added to scavenge electrons suppressed the main-chain scission efficiently without affecting the formation of volatile products from the ester side chain. The above reaction model motivated us to apply the ESE method to the study of radicals in irradiated PMMA. The model now seems inadequate, because it cannot accommodate some recent ESE results as mentioned later. 

In the course of the reactions, the other functional groups are also derivatized. Hydroxyamino acids and Tyr react with alkyl chloroformate with the formation of carbonate esters, Cys and CysH provide thiocarbonates, and the imidazole nitrogen of His is also protected. The indole functional group of Try does not change, Pro forms a stable carbalkoxydithiocarbamate and Arg does not provide any volatile product. The derivatives were separated successfully (except the pair Leu-De) on 5% of QF-1 with temperature programming (94-235°C). The reproducibility of the method was stated to be 5%. Using an FID and ECD, 10-10 and 10-13 mol of amino acids, respectively, can be determined. 

Acetals and ketals having a second junctional group ate made by these procedures. For example, acrolein reacts with ethyl orthoformate in alcohol solution with ammonium nitrate as catalyst to give acrolein diethyl acetal (73%). On the other hand, it reacts with ethyl ortho silicate with anhydrous hydrogen chloride as catalyst to furnish (i-ethoxypropionaldehyde diethyl acetal (76%). p-Bromoacetophenone and ethyl orthoformate give the corresponding ketal in 65% yield. p-Methoxy- and m-amino-benzaldehyde diethyl acetals are made in a similar way in 96% and 85% yields, respectively. a-Keto esters like ethyl a-keto-n-butytate and ethyl a-keto-tr-valetate are converted to their diethyl ketals in excellent yields by the action of orthoformic ester in ethanol-hydrochloric acid solution. If the reaction is carried out in the presence of ethylene glycol instead of ethanol and, in addition, the volatile products are removed by distillation, then the ethylene ketal is formed in almost quantitative yield (cf. method 133). 

Scission of LO Beta-scission of alkoxyl radicals leads to scission of the C—C bond on either side of the LO group to yield a mixture of carbonyl products and free radicals, typically aldehydes, alkanes, and oxo-esters, from the initial alkoxyl radicals (297). Scission produces the volatile products so characteristically... 

The aromatic acids released from different HA upon pyrolysis in the presence of TMAH probably represent original components of the HA structure released by the thermolytic action of TMAH (10,12,16,17). This observation is supported by the TMAH thermochemolysis data of Hatcher et al. (23) and Hatcher and Clifford (16) for a volcanic soil humic acid. In fact, the C-NMR spectrum of this particular HA (shown in Figure 4) clearly indicates that it is composed of only aromatic and carboxyl carbons. Conventional pyrolysis of these HA produced trace quantities of volatile products without the release of any significant compounds while pyrolysis in the presence of TMAH yielded mainly benzenecarboxylic acid methyl esters (Figure 5), in accordance with the NMR data. 

Volatile product accumulation kinetics in cultures of Kluvveromvces strains includes short chain alcohols and esters such as 2 phenylethyl acetate. These cultures typically have a fruity,... 

Figure 5 shows the influence of harvest time and storage on total volatiles production. Since the production of many but not all of the aroma volatiles is linked to amino acid precursors it may be expected that the total volatiles behavior may reflect that of the amino acids especially those which supply many of the carbon skeletons for the esters found in melons. The pattern of behavior for the total volatiles is generally in accord with that of these amino acids and does very clearly illustrate the profound influence of harvest time on the generation of the aroma profile. Fruit harvested only two days before folly ripe develops only about one quarter of the total volatiles concentration shown a few days postharvest, by a folly ripe sample. This rather dramatic difference may reflect the inability of prematurely harvested fiuit to accumulate sufficient concentrations of required volatiles substrates because certain metabolic responses have not been activated. 

Pyrolysis with in situ methylation in the presence of TMAH is now commonly applied for the structural investigation of HS. It has been reported, however, that TMAH not only methylates polar pyrolysate but also assists in bond cleavage. For example, TMAH was found as effective at 300°C as at 700°C for the production of some volatile products from HS, indicating that pyrolysis occurs with equal effectiveness at subpyrolysis temperature of 300°C. It is believed that TMAH pyrolysis is actually a thermally assisted chemolysis rather than pure pyrolysis and it can cause hydrolytic ester and ether bond cleavage even at lower temperature, resulting in some unwanted side reactions, e.g., artificial formation of carboxylic groups from aldehydes. Therefore, TMAH thermochemolysis at low temperature, e.g., 300°C has been proposed. This technique offers several advantages over classical flash pyrolysis or preparative pyrolysis apparatus " ... 

It might be noted that Michaelis-Arbuzov reactions between the esters 166 and Mel or EtI yield the products 170(R = Me or Et), and whilst benzyl chloride affords the expected Michaelis-Arbuzov ester 171, the outcome of a reaction with benzyl bromide depends on the experimental conditions, the ester 171 being formed at 100 °C with removal of volatile products at 100 mmHg, but at 130 °C in a sealed tube the product is 170 (R = CH2Ph) l... 

---