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The Nature of Tetrazolium Salts and Formazans.

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ketones. If (If) is heated for 48 h at 130 O C the radioactivity
is distributed equally between C-1 and C-5. However, the
data collected up to the present suggest that two halogen
substituents on C-5 are essential for complete and irreversible pentadiene 1,5-halogen-oxygen exchange: the cis-form
of ( l g ) appears merely to enter into an equilibrium with the
pyran ( 2 g ) ; the presence of the ketone (3g) in the mixture
cannot be ascertained
I f complex-forming reagents (FeCI3 or SnC14) are added to
( I ) during the rearrangement, pyrylium salts can be isolated
in good yieldr41, a fact that presents strong evidcnce for formation of the pyrans (2) as intermediates.
[Lecture at Saarbriicken (Germany), Jan. 21st, 19661
[VB 988 IE]
German version: Angew. Cheiii. 75, 722 (1966)
[ I ] A. Roedig, AngeLv. Chcm. 76, 276 (1964), Anye:v. Chem.
internat. Edit. 3. 317 (1964).
[2] A . Roedig and G . Ma/-/il, Liebig Ann. Cheni. 659, 1 (1962);
A . Roedig, R.Koli/liaupt, and G.Markl, Chem.Ber.99, 698 (1966).
[3] / I . G. Viehe, Chem. Bcr. 9.7, 1697 (1960); Angew. Chem. 75,
793 (1963), Angew. Chcm. internat. Edit. 2, 622 (1963); If. G.
Vielie and E. Froncl?iniont, Chem. Ber. 96, 3153 (1963); H . C.
P’ielie, J . Dole, and E. Fraricliiiiiont, ibid. 97, 211 (1964).
[4] A . Roedig, M . Schlosser, and H . - A . Rerik, Ange:v. Chem. 78.
448 (l(966);Angew. Chem. internat. Edit. 5, 418 (1966).
The Nature of Tetrazolium Salts and Formazans
shift in the frequency of the C-N valence vibration from
1226 to 1236 cm-1 are observed on passing from a substituent
with a (+)-M effect to one with a (-)-I effect. These findings
are indicative of a n increase in the clectron density in the
N=C-N portion of the molecule and of an expansion along
the N-H.-.N bonds associated with a weakening of the
hydrogen bond. Consequently, the C-aryl residue and the
“heterocycle” appear to be almost coplanar whereas both
the hydrogen bridge and the N-aryl residues are not in a
coplanar arrangement. In principle, therefore, the same
picture is obtained for formazans as for tetrazolium salts,
namely that the C-aryI substituent exerts a significant
influence o n the bonding and o n the ring parameters in
remote parts of the molecule.
[Lecture at Isny (Germany), April 20th, 19661
[VB 994 1EI
German bersion: Angew Chem. 78, 683 (1966)
C. Schiele, Ulm (Germany)
The concensus of opinion regarding the nature of tetrazolium
salts was summarized by Nineham 111 who formulated them
as resonance hybrids between the structures ( l a ) and (Ib).
However, from the observation of V C = N ( I ) and VC-N(4)
vibrations at 1527-1544 cm-* and near 1150 cm-1 we were
able to establish that the system is not a resonance hybrid
but occurs exclusively in the form ( l a ) .
Furthermore, it could be shown that there is a marked
influence of aryl substituents on the carbon atom of the
tetrazolium ring upon the ease of reduction of these compounds (measurement of the decomposition potential o n
Ag/Pt); this effect could even be used occasionally, e.g. when
R = R = p-tolyl or p-chlorophenyl and R”= phenyl, or
when R = R” = p-tolyl or p-chlorophenyl and R’=
phenyl, to differentiate between N(2)- and N(3)-substituted
tetrazolium salts. These findings led to the postulation of a
heterocycle with varying bond lengths between the N-2 and
N-3 atoms of the ring, depending on the nature of the aryl
substituent on the carbon atom in the ring. The occurrence
of two modifications with each of eight solid tetrazolium
perchlorates indicated the existence of tetrazolium salts which
are stereoisomeric with regard to the arrangement of the aryl
residue. The infrared spectra of these forms differ in the
regions of their skeletal, YC-H, and ring deformation vibrations. They also give different Debye-Scherrer diagrams and
different extinction coefficients in the ultraviolet and visible
regions.
The occurrence of stereoisomers does not, however, explain
why crystalline tetrazolium salts turn yellow when exposed
to light. This discoloration is attributed by Nineham [ I ] to
some structural characteristic of the compounds, but no
explanation is given. The new absorption bands that appear
between 400 and 450 mu. when layers of tetrazolium salts are
irradiated can be interpreted when a photoisomerism caused
solely by a change in position of the anion is assumed. This
Aiigew. Clrem. internaf. Edit.
interpretation finds support in the results of infrared spectroscopic investigations.
Formazans (2) also exhibit a marked change in frequency of
the C-N valence vibration in dependence o n the C-aryl
substituent. If formazans are examined in which only the
C-aryl substituent is varied, a n increase in the extinction of
the chroinophoric band from log E = 4.1 to log E = 4.2 and a
Vol. 5 (1966) 1 No. 7
[ I ] A . W . h’irreho/ii, Chem. Reviews 55, 355 (1955).
New Facts about Aroma Essences
F. Dmwert, Siebeldingen (Germany)
It was established using gas chromatography and radio-gas
chromatography that there are considerable differences
between the substances that cause the aromas of fruit and
those of fruit juices prepared from the fruit. The fruity esters
of apples (butyl acetate, amyI acetates, hexyl acetate, etc.)
are split to varying degrees by hydrolases after damage of
the fruit cells. Simultaneously enzymatic oxidations occur in
the damaged (homogenized) fruit which lead to the formation
of new aroma essences, which include 2-hexenal ( I ) and
hexanal (2) in predominant proportions; these compounds
therefore play a major part in determining the aroma and
taste of apple juice. The precursor of ( I ) is linolenic acid,
that of (2) is linoleic acid [I].
Numerous aroma essences are produced by yeast. The
amounts of such substances vary when the sugar content of
the fermentation solution is kept constant but its amino-acid
content is varied. Model fermentations with Succharomyces
cerevisiae in a n otherwise uniform culture medium revealed
that various amino acids contribute differently to the formation of aroma substances in the yeast. Methionine and
proline cause a higher formation of malic and tartaric acids
relative to other amino acids.
[Lecture at Freiburg (Germany), April 29th, 19661
[VB 993 IE]
German version: Angew. Chern. 78, 683 (1966)
[ I ] F. Drorvert, W . I-leimonn, R. Emberger, and R. Tress/, Liebigs
Ann. Chem., in the press.
Transfer of Diazo Groups:
Mechanism and Preparative Importance
M. Regizz, Saarbrucken (Germany)
Transfer of diazo groups from sulfonyl azides ( I ) to active
methylene compounds (2) occurs by exchange of the N2
group of the azide for two H atoms of the methylene com-
68 1
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