close

Вход

Забыли?

вход по аккаунту

?

Electrochemical Reactions at Semiconductor Surfaces.

код для вставкиСкачать
Heterocyclic Diazo-azo Compounds as a Source
of Nucleophilic Carbenes [*I
H . Balli, Marburg/Lahn (Germany)
Heterocyclic-diazo-azo compounds (tetrazo compounds) (2),
a new class of mesomeric compounds of the benzthiazole
series, can be prepared from the azidinium salts ( I ) [l] and
lithium azide at ca. -50 "C.
The "azohomologous" diazo compounds (2), which are
explosive in the dry state at room temperature, are protonated by HBF4 a t -50 "C with elimination of nitrogen (2 N2)
to give the benzthiazolium salts (5). At ca. -1O'C in tetrahydrofuran or dimethylformamide, compounds (2) undergo
controlled decomposition to give the nucleophilic heterocyclic carbenes (3); these can be trapped by tetracyanoethylene, azidinium salts ( I ) , and diazonium salts to give
respectively, cyclopropane derivatives, triazatrimethinecyanines [ 2 , 3 ] and quaternary heterocyclic azo dyes [3,4].
I
(2)
C2H5
-
The kinetics of the process ( I ) + (2)
(3) + triazatrimethinecyanine (X = H) confirm the existence of the shortlived intermediate (3) (cf. in contrast [4]). As shown in the
[*] See also H . Quast and S. Hiinig, Angew. Chem. 76, 989 (1964);
Angew. Chem. 3, 800 (1964).
[I] H . Bulli and F. Kersting, Liebigs Ann. Chem. 647, 1 (1961).
[2] H . BuNi and F. Kersting, Liebigs Ann. Chem. 663, 96, 103
(1963).
[3] H . Bulli, Angew. Chem. 70, 442 (1958).
[4] H . W. Wanzlick and H. J. Kleiner, Angew. Chem. 75, 1204
(1963); Angew. Chem. internat. Edit. 3, 65 (1964).
case of X = NO2, a true dimerisation of the nucleophilic
carbenes, (3) -+ (4), could not be observed (cf. in contrast
[41). Compound (4) may be readily prepared via ( 5 ) or (6).
The configuration of ( 4 ) is unknown.
[GDCh-Ortsverband Krefeld (Germany),
September 17th, 19641
[VB 860/164 IE]
German version: Angew. Chem. 76, 995 (1964)
Electrochemical Reactions at Semiconductor
Surfaces
H . Gerischer. Munchen (Germany)
The role that the bonding state of the electrons in a solid
plays in the mechanism of surface reactions may be most
clearly followed when the electrons are direct reactants. This
can be demonstrated by electrochemical reactions such as
anodic dissolution, cathodic evolution of hydrogen, or other
redox reactions at the surfaces of semiconductors. During
anodic dissolution of Ge, Si, and GaAs, holes are consumed in the rate-determining step, i. e. the release
of surface atoms is initiated by donation of the bonding
electrons to vacant electronic states in the valence band.
In germanium, some of the four electrons per surface
atom, which are given free from bonding states during oxidation, are transferred to the conduction band. In semiconductors with a larger band gap, e . g . Si or GaAs, the latter
step is no longer possible and the release of atoms from the
lattice results solely by uptake of holes.
In redox reactions one can discriminate between electron
transfers involving either electrons of the conduction band
or electrons of the valence band. For example, electrons
from the conduction band are consumed during cathodic
hydrogen discharge at all the three semiconductors mentioned. On the other hand, reduction of Fe3+ ions at these semiconductors takes place by uptake of electrons from the
valence band.
Comparison of the work functions for theemission of electrons
from the conduction band, the valence band, and the components of the redox system suggests that electron exchange
in the conduction band should be favored in redox systems
with reducing properties, i . e . with a negative redox potential
and a correspondingly lower electron affinity. Electron
exchange in the valence band is preferred for redox systems
with high redox potential, i. e. with a greater electron affinity.
This theoretically expected result is confirmed by experimental findings.
[GDCh-Ortsverband Freiburg-Sudbaden (Germany),
[VB 843/162 IE]
July loth, 19641
German version: Anpew. Chem. 76, 759 (1964)
SELECTED ABSTRACTS
Isocyanates of sulfuric acid react with dimethyl sulfoxide, according to R . Appel and H , Rittersbacher, to form sulfuryldimethylsulfimines with elimination of COz. Amine oxides
form adducts with sulfuryl di-isocyanate, which can be split
up into their components again by chemical means. A colorless oil, which decomposes explosively above 0 " C , can be
isolated from the reaction of the isocyanates of sulfuric acid
with dimethyl sulfoxide under mild conditions below 0 "C.
Sulfurylbisdimethylsulfimine ( I ) , m.p. 177 "C, is formed in
54 % yield, with evolution of CO2 and heat, when sulfuryl
di-isocyanate is treated with dimethyl sulfoxide at 20 "C.
OzS(NC0)l
+ 2 OS(CH&
-+
(CH&S=N-S02-N=S(CHp)2
(1)
Dimethylsulfiminosulfuric acid, m.p. 171 OC, is formed in
75 % yield by hydrolysis of the product obtained from chlorosulfonyl isocyanate and dimethyl sulfoxide. The adduct of
pyridine N-oxide and sulfuryl di-isocyanate melts at 138 to
139 "C, the trimethylamine N-oxide adduct melts at 68 "C.
Angew. Chem. internat. Edit.
Vol. 3 (1964) No. I 2
Water decomposes the adducts, occasionally with the appearance of flames, to give sulfamide, C02, and the N-oxide. /
Chem. Ber. 97, 852 (1964) / -W.
[Rd 996/280 IE]
The adsorption of cyanine dyes onto silver halides has been investigated by J. F. Padday. The surface occupied by dyestuff
molecules adsorbed o n different silver halides is not always
the same; this causes problems in the use of such dyes for
estimating surface areas. The absorption spectrum of the adsorbed dyestuff also depends on the silver halide carrier and
furthermore on the degree of coverage of the surface. Different absorption bands were found which can be ascribed to
monomeric (M bands), dimeric ( D or H bands), and polymeric (J bands) species of the dyestuff. The occurrence of H
or J bands depends pracitcally exclusively o n the conditions
of adsorption, and not upon the degree of coverage of the surface. It is therefore concluded that the association theory must
be reexamined. / Trans. Faraday SOC.60, 1325 (1964) / -Hz.
[Rd I13/300 IE]
809
Документ
Категория
Без категории
Просмотров
1
Размер файла
133 Кб
Теги
reaction, semiconductor, surface, electrochemically
1/--страниц
Пожаловаться на содержимое документа