Glyoxal, Table

Acetals of A. A -dimethyl hydrazones 4, derived from glyoxal (1) and various enantiomerically pure diols (c.g., 3a-f)24, are readily prepared by transacetalization of 2. Addition of methyl-or butyllithium to 4 provides the corresponding hydrazines in good yield (70-88%) and moderate to excellent diastereoselectivity (see Table 3)4,5. 

French researchers [38c] have investigated the /zetero-Diels-Alder reaction of methylglyoxylate and glyoxal monoacetal with 2-methyl-1,3-pentadiene in a microwave oven under various reaction conditions (Table 4.9). The microwave (MW) irradiation does not affect the diastereoisomeric ratio of adducts trans/cis = 70 30) but dramatically reduces the reaction time. The glyoxal monoacetal, for instance, gives 82 % adducts after 5 minutes when submitted to irradiation with an incident power (IP) of 600 W in PhH and in the presence of ZnCL (Table 4.9, entry 1), while no reaction occurs if carried out for 4h at 140 °C in sole PhH. Similarly, methylgloxylate in water at 140 °C gives 82% adducts after 3h, whereas microwave irradiation reduces the reaction time to 8 minutes (Table 4.9, entry 5). 

Table 4.9 Diels-Alder reactions of glyoxal derivatives promoted by microwaves under different experimental conditions...

Under the right conditions, glyoxal fixatives form adducts with the same groups listed for formaldehyde (Table 12.1). We do not know if compound... 

The results of ab initio calculations of glyoxal and acrolein are shown in Table 20. The low cis-trans energy difference in acrolein may be a result of hydrogen bonding which obtains only in the cis conformation as illustrated below ... 

Table 20. Computed relative energies of the cis and trans conformations of glyoxal and acrolein...

Allenyltrimethylsilanes add to ethyl glyoxalate in the presence of a chiral pybox scandium triflate catalyst to afford highly enantioenriched homopropargylic alcohols or dihydrofurans, depending on the nature of the silyl substituent (Tables 9.39 and 9.40) [62]. The trimethylsilyl-substituted silanes give rise to the alcohol products whereas the bulkier t-butyldiphenylsilyl (DPS)-substituted silanes yield only the [3 + 2] cycloadducts. A bidentate complex of the glyoxalate with the scandium metal center in which the aldehyde carbonyl adopts an axial orientation accounts for the observed facial preference ofboth additions. 

It is conceivable that a carbonyl compound with an n,n triplet energy lower than that of benzophenone could yield the photocycloaddition product in some of these cases. A reaction which may illustrate this point is the photocycloaddition of ethyl glyoxylate to styrene and 1,1-diphenylethylene.66 Unfortunately, the triplet energy of ethyl glyoxalate has not been measured however, there is adequate reason to believe it is lower than that of benzophenone (see Table VI). 

To enhance the shelf life of finished paper product, the step 1 product was applied below its critical micelle concentration (CMC). Materials additized above the CMC formed insoluble gels when aged for 8 days at 73°C. The CMC ranges was determined using glyoxalated poly(vinylamide-co-diallyldimethyl-ammonium chloride) containing 90 wt% vinylamide and are provided in Table 1. 

TABLE 1. Critical Micelle Concentration and Tensile Strength Testing Results for Glyoxalated Poly(vinylamide-co-diallyldimethylanunonium chloride)... 

Table 58 gives the formation constants for silver(I) complexes of acetone thiosemicarbazone and glyoxal dithiosemicarbazone (55).443 In the latter case, the ligand was found to be suitable for the photometric determination of silver at pH 1 1, in the presence of EDTA. The effective molar absorptivity was 43 000 cm2 mmol-1 at 335 nm.443... 

Table 9 Glyoxal ground-state energies, cis-trans separation, and rotational barrier...

Components were identified with GC/MS. A thiazolidine derivative is easily identified using single ion. monitoring with m/z 88 (thiazolidine ring - H). Table II shows mass spectra and GC retention data of thiazolidine derivatives. The gas chromatogram of the extract from the reaction mixture indicated that methyl glyoxal produced three products, 2-acetylthiazoline (peak 7), 2-acetylthiazolidine (peak 8), and 2-formyl-2-methylthiazolidine (peak 9). 

Reaction temperature. The same molar ratio of methyl glyoxal and cysteamine was reacted at 0, 25, and 100°C. The results are shown in Table III. The reaction at room temperature (20°C) gave the best results for 2-acetylthiazolidine formation. 

Table III. Relative ratio of products from the reaction of methyl glyoxal and cysteamine at various temperature...

The effect of molar ratio of methyl glyoxal and cysteamine. This was examined at room temperature and the results are shown in Table IV. When the molar ratio of cysteamine and methyl glyoxal was 1000 at pH 8, 2-acetylthiazolidine was produced exclusively. On the other hand, formation of 2-acetylthiazolidine remained constant pH 6. Therefore, cysteamine was reacted with samples of interest at 25°C and in a quantity to exceed 1000 fold the estimated amount of methyl flyoxal in the following experiments, when experiment was cunducted at pH 8. 

The results of formaldehyde and methyl glyoxal analysis in commercial foods are shown in Table VIII. Formaldehyde was identified in the levels of 3.7-17 ppm in coffee obtained from various commercial sources. It was found at higher levels in instant coffees than in brewed coffee. This suggests that formaldehyde may escape from coffee during brewing. Formaldehyde has been reported in coffee volatiles by several researchers (31). There are however, no reports on quantitative analysis of formaldehyde in coffee prior to the present study. 

Table IX shows the calculated values of methyl glyoxal intake for each food item when it is consumed. Even after dilution, coffee provided the most methyl glyoxal intake. It is difficult to estimate formaldehyde or methyl glyoxal intake from soy sauce because its use varies widely.

An interesting consideration relating to the influence of acidity in the reaction medium is derived from the comparison between the conditions adopted for the synthesis of the P-aminoketoncs 44 and 45, and tho.se required for the analogous derivatives that lack the carboxy group. Whereas the latter compounds are prepared under the. severe conditions of type A (Table 6), both the syntheses of 44, employing glyoxal as aldehyde reagent,and that of 45, which is prepared from 3-benzoyl propionic acid, take place readily under mild conditions (type B or C). 

The complexity of the reaction products at low temperatures is shown by the results of Blacet and Blaedel" , obtained at 2654 A and at temperatures extending down to —40 °C. Some of their results are summarised in Table 10. No methyl-glyoxal was detected. 

The reactions of glyoxal at 100° and pH 5 with dipeptides (380, 381) and tri-and tetrapeptides (382) to give some 2-oxo-l, 2-dihydropyrazines are summarized in Table 11.8 and discussed in greater detail in Section 7. 

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