Pent-2-enal

The alkoxide doesn t have to be made first, though, because alcohols dissolved in basic solution are at least partly deprotonated to give alkoxide anions. How much alkoxide is present depends on the pH of the solution and therefore the pKa of the base (Chapter 8), but even a tiny amount is acceptable because once this has added it will be replaced by more alkoxide in acid-base equilibrium with the alcohol. In this example, allyl alcohol adds to pent-2-enal, catalysed by sodium-hydroxide in the presence of a buffer. 

Fig. 5.12. HPLC separation of a reference mixture of alk-2-enals. The numbers indicate the chain length of the aldehyde, thus 4 but-2-enal 5 pent-2-enal etc. (Benedetti et...

There is no direct experimental evidence for this complex decomposition and it may well occur by several steps [107]. However, substantial yields of unsaturated carbonyl compounds are formed particularly at high pressures [78] under initial reaction conditions where cool flames propagate. For example, the cool-flame oxidation of 2-methylpentane at 525 °C and 19.7 atm in a rapid compression machine [78] yields no less than 14 unsaturated carbonyl compounds viz acrolein, methacrolein, but-l-en-3-one, pent-2-enal, pent-l-en-3-one, pent-l-en-4-one, trans-pent-2-en-4r one, 2-methylbut-l-en-3-one, 2-methylpent-l-en-3-one, 4-methylpent-l-en-3-one, 2-methylpent-l-en-4-one, 2-methylpent-2-en-4-one, 2-methyl-pent-2-enal and 4-methylpent-2-enal. Spectroscopic studies of the preflame reactions [78] have shown that the unsaturated ketones account for ca. 90 % of the absorption which, occurs at 2600 A. At lower initial temperatures and pressures acrolein and crotonaldehyde are formed from n-pentane [69, 70] and n-heptane [82], and acrolein is also formed from isobutane [68]. 

In contrast the reaction of a 1 1 molar mixture of i50-butanal and n-butanal ran successfully for 20 hours with no gross carbon laydown on the discharged catalyst (3.1 wt%). The products formed were 2-ethyl hexenal as expected from the self-condensation reaction of n-butanal and 2-ethyl-4-methyl-pent-2-enal, the dehydrated product from the crossed aldol reaction of n and /50-butanal (Table 6). The overall selectivity of this reaction to aldol products is lower than the selectivties achieved with crushed 4 wt %... 

The lachrymatory factor in onion (thiopropanal-S-oxide) is considered to come from the S-l-propenyl-cysteine sulfoxide precursor [40]. Thiopropanal-S-oxide (CH3-CH2-CH=S=0) is unstable reacting with pyruvate to form propanol, 2-methyl pentanal and 2-methyl pent-2-enal [41]. It is of interest that no lachrymatory properties were found in 25 species of wild onions [42]. This would suggest that the 1-propenyl precursor may be absent from the wild onion. 

Alkanals (C5—C7) hex-2-enal 2,4-dienals (C5-C10) 2-/-pentenylfuran Alkanals (C5—CIO) alk-2-enals (C5—CIO) hepta-2-t,4-t-dienal 2-heptanone pent-2-/-enal but-2-/-enal... 

Z)-pent-2-enal malondialdehyde (enol form) 9-oxononanoio acid... 

E)-Pent-2-enal Oily, greasy, green Linolenic acid... 

The composition of volatiles of juices and beverages prepared from the oils extracted from citrus fruit peels is slightly different. For example, juices contain ethyl vinyl ketone, ( )-pent-2-enal and ethyl butanoate as major aromatic substances. 

Thiets react with cyclopentadienylcobalt dicarbonyl to yield complexes of thioacroleins, which are valence tautomers of thiets. Oxidation of 3-ethyl-4-methylthiet and 3-propyl-4-ethylthiet with hydrogen peroxide in acetic anhydride did not give the S-oxides, but instead 2-ethylbut-2-enal and 2-propyl-pent-2-enal, respectively. ... 

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