186 Applications and Occurrences of Heterocycles in Everyday Life
Classical primary explosives are often heavy metal salts, such as lead azide (Pb(N 3 ) 2 ) or lead styphnate (the lead
salt of 2,4,6-trinitroresorcinol (2,4,6-trinitrobenzene-1,3-diol)), which can cause pollution problems, particularly
on fi ring ranges. A number of heterocyclic compounds are being developed to avoid this ‘heavy metal problem’.
4,6-Dinitrobenzofuroxan (DNBF; 4,6-dinitro-2,1,3-benzoxadiazole) is a widely used primary explosive and it is
notable that it is used for this purpose as its potassium salt, which is actually a Meisenheimer complex (KDNBF). It
is a replacement for lead styphnate. Amine salts of 5-nitrotetrazole have also been proposed as ‘Green’ alternatives
for detonators.
Food and drink
Heterocycles are signifi cant components of foods, as nutritionally important constituents, as colouring agents and
as fl avours and aromas. Many of these are present in raw foods but some are ‘additives’ (natural or synthetic) or are
formed during cooking – the kitchen is a site of extensive heterocyclic synthesis!
We also consume, in all foods, large numbers of other compounds of no nutritional benefi t, which just happen to be
there naturally. Most of these are relatively innocuous but some can produce adverse effects in certain circumstances
(see page 192, divicine). Other compounds can be pleasingly psychoactive: caffeine is a well-known component of tea
and coffee but the less well-known, closely-related theobromine is a major constituent of chocolate.
Food fl avour and aroma components include many pyrazines and furans, with signifi cant contributions from thiazoles
(which can have similar aromas to pyrazines) and thiophenes. Many of these simple aroma compounds can be detected
(smelt) down to very low levels (ppb or even less). Also, depending on concentration, the same compound may show a
range of aromas. The overall fl avours and aromas are generally the sum of the effects of complex mixtures.
The most important natural aroma compounds in raw foods are probably pyrazines, which tend to be simple alkyl and
methoxy derivatives. They occur in fresh vegetables such as peas and capsicum peppers, and in many grape and wine
aromas. Amongst other important products, furfuryl mercaptan is the main aroma compound in coffee. Signifi cant
non-aromatic furanones include sotolone, a naturally-occurring compound, which is also used to fl avour artifi cial
maple syrup (it has a maple aroma at low concentration and fenugreek at higher concentrations) and furaneol, whose
alternative name ‘strawberry furanone’ explains everything.