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New Investigations of Heterocumulenes and their Derivatives.

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Use of X-ray and electron diffraction led to recognition of
the crystal species a-FezOJ (hematite) and CaCuSi401~(the
ancient synthetic pigment “Egyptian blue”), as well as
calcium carbonate, but other colored material lay below the
limits of detection. However, the fine structure of the electron
diffraction of extracts from surface prints of green fragments
and yellow fragments gave indications of the presence of
clay mineral structures.
Ground sections showed their layer structure in the electron
microprobe. Element concentration profiles confirmed the
X-ray findings and led to the additional conclusions that the
colored bodies in the green pigment layers were glauconite
and that those in the yellow pigment layers were an ocher
(kaolinite with a-FeOOH).
From the thickness of the pigment layers of the various fragments it was further concluded that the blue layers were
purposely applied more thickly, so that the full color tone of
the coarsely crystalline Egyptian blue became clearly evident;
our imitation of Egyptian blue, when powdered in a mortar,
is pale blue and does not possess the deep color tone of the
crude product. Such fragments thus cannot be deemed “fresco
buono” in the strictest sense.
The instrumentation used has proved useful for characterization of the composition and intimate structure of such
fragments of paintings and similar objects.
[VB 146 IE]
Lecture at Bern, on February 2, 1968
German version: Angew. Chem. 80, 494 (1968)
[*] Dr. R. Giovanoli
Institut fur anorganische, analytische und
physikalische Chemie der Universitat
CH-3000 Bern, Freiestr. 3 (Switzerland)
[l] W.Klinkert, Mitt.dtsch. arch.Inst., Rom. Abt. 64,111 (1957).
121 U.Hofmann, Angew. Chem. 74, 397 (1962); Angew. Chem.
internat. Edit. I , 341 (1962).
Porphin Derivatives as Experimental Models for
Mass-spectroscopic Fragmentation Reactions
By H , Budzikiewicz [*I
As a result of the concept that decomposition of a molecule
during mass-spectroscopy is induced by a localized positive
charge, such study of organic compounds has in recent years
concerned mainly the influence of various functional groups
and structural units on the fragmentation pattern. To obtain
a more general picture it is necessary to test the available
results for applicability to complex systems and for their
limitations. Porphin derivatives are suitable as experimental
models because in all their decomposition reactions the
positive charge is localized preferentially in the x-system of
the macrocycle whilst fragmentation occurs in the side chain.
In the case of 1,2,3,4,5,6,7,8-octaethyl-l,2,5,6-tetrahydroporphin the preferential formation of even-numbered electron
systems in the singly and doubly charged regions can be
demonstrated by comparing the relative intensities of the
daughter ions formed by successive loss of ethyl radicals;
this is also indicated by the preferred course of the Mctafferty
rearrangement which affords ions with even numbers of
electrons. The mass spectra of porphyrins and chlorins that
are not substituted in the meso-position confirm the principle
of benzyl cleavage observed with simple aromatic compounds
whilst the mutual steric hindrance of the side chains in 6,y,7substituted compounds causes fission of the bonds leading
directly to the aromatic ring and also leads to simultaneous
loss of two substituents with formation of a metastable peak.
The last-mentioned observation is of particular importance
for the theory of metastable transitions. Comparison of the
mass spectra of 10-methoxy- and 10-isopropoxy-methylpheophorbide indicates the limits within which analogies
may be drawn o n purely empirical application of mass
spectroscopy: the differing behavior of the two types of
Angew. Chem. internat. Edit. / Vol. 7 (1968) 1 No. 6
compound can be explained by the fact that the energetics
of cleavage of various bonds proceeding from the same center
(C-10) may be more or less favorable according to the nature
of the substituents.
Lecture at Braunschweig (Germany) on February 5 , 1968 [VB 147 1El
German version: Angew. Chem. 80,495 (1968)
[ * ] Doz. Dr. H. Budzikiewicz
Institut fur Organische Chemie der Technischen Universitat
33 Braunschweig, Schleinitzstr. (Germany)
New Investigations of Heterocumulenesl**land
their Derivatives
By R . Neidlein [*I
N-Acylcarbamoyl azides ( I ) are converted by loss of nitrogen
into 1,2,4-0xadiazol-3-ofs (Z), whose structure is proved by
degradative reactions and by I R and IH-NMR spectroscopy, as well as by synthesis of their methyl ethers by another route. The tetrazole-5-thiols (3), that can be obtained
from isothiocyanates and hydrazoic acid with subsequent
rearrangement, are converted by way of the intermediate ( 4 )
into the quasiaromatic thiazol0[3,Zd]tetrazolylium salts
[isolated as perchlorate (S)], whose properties and reactions
have been intensively studied.
(7)
Whereas reaction of N-(dichloromethy1ene)carboxyamides
( 6 ) with electrophilic metal chlorides such as SbC1s gives
N-acylchloroformonitrilium salts (71, only addition products
can be obtained from N-(dichloromethy1ene)sulfonamides
and electrophilic metal chlorides. Also, N- [(alkylthio)chloromethylene]sulfonamides cannot be converted into the corresponding nitrilium salts but decomposition reactions occur
in which are formed sulfonyl chlorides and adducts of the
electrophilic metal chlorides to the alkyl thiocyanates that are
split off. Further syntheses with N-(dichlorornethy1ene)sulfonamides lead to substituted 1,3.4-oxadiazoles, 1,3,4thiadiazoles, tetrazoles, 1,2,4-oxadiazoles, 1,2,4-triazoles,
etc.
Lecture at Bonn (Germany) on February 6, 1968
[VB 149 IE]
German version: Angew. Chem. 80, 496 (1968)
[*I Prof. Dr. R. Neidlein
Pharmazeutisch-Chemisches Institut der Universitat (TH)
75 Karlsruhe, Kaiserstr. 12 (Germany)
[**I Byheterocumulenes are meant compounds having cumulated
double bonds, and whose C atoms are replaced by heteroatoms,
e.g. isocyanates, carbodiimides, thionylimines, etc.; cf. H . Ulrich:
Cycloaddition Reactions of Heterocumulenes. Academic Press,
New York-London 1967.
479
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