Diazene
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Diimide, also called diazene or diimine, is a compound having the formula (NH)2. It exists as two
geometric isomer Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is ...
s, ''E'' (''trans'') and ''Z'' (''cis''). The term diazene is more common for organic derivatives of diimide. Thus,
azobenzene Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond. It is the simplest example of an aryl azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of simi ...
is an example of an organic diazene.


Synthesis

A traditional route to diimide involves oxidation of hydrazine with hydrogen peroxide or air. Alternatively the hydrolysis of
diethyl azodicarboxylate Diethyl azodicarboxylate, conventionally abbreviated as DEAD and sometimes as DEADCAT, is an organic compound with the structural formula CH3CH2O2CN=NCO2CH2CH3. Its molecular structure consists of a central azo functional group, RN=NR, flanked ...
or
azodicarbonamide Azodicarbonamide, ADCA, ADA, or azo(''bis'')formamide, is a chemical compound with the molecular formula C2H4O2N4. It is a yellow to orange-red, odorless, crystalline powder. It is sometimes called a 'yoga mat' chemical because of its widespread u ...
affords diimide: :(NCOOH)2 → (NH)2 + 2 CO2 Nowadays, diimide is generated by thermal decomposition of 2,4,6‐triisopropylbenzenesulfonylhydrazide. Because of its instability, diimide is generated and used ''in-situ''. A mixture of both the ''cis'' (''Z-'') and ''trans'' (''E-'') isomers is produced. Both isomers are unstable, and they undergo a slow interconversion. The ''trans'' isomer is more stable, but the ''cis'' isomer is the one that reacts with unsaturated substrates, therefore the equilibrium between them shifts towards the ''cis'' isomer due to
Le Chatelier's principle Le Chatelier's principle (pronounced or ), also called Chatelier's principle (or the Equilibrium Law), is a principle of chemistry used to predict the effect of a change in conditions on chemical equilibria. The principle is named after French c ...
. Some procedures call for the addition of carboxylic acids, which catalyse the cis–trans isomerization. Diimide decomposes readily. Even at low temperatures, the more stable ''trans'' isomer rapidly undergoes various disproportionation reactions, primarily forming hydrazine and
nitrogen gas Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...
: :2 HN=NH → H2N–NH2 + N2 Because of this competing decomposition reaction, reductions with diimide typically require a large excess of the precursor reagent.


Applications to organic synthesis

Diimide is occasionally useful as a reagent in organic synthesis. It hydrogenates alkenes and alkynes with selective delivery of hydrogen from one face of the substrate resulting in the same stereoselectivty as metal-catalysed ''syn'' addition of H2. The only coproduct released is nitrogen gas. Although the method is cumbersome, the use of diimide avoids the need for high pressures or hydrogen gas and metal catalysts, which can be expensive. The hydrogenation mechanism involves a six-membered C2H2N2 transition state: :


Selectivity

Diimide is advantageous because it selectively reduces alkenes and alkynes and is unreactive toward many
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
s that would interfere with normal
catalytic hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
. Thus,
peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen ...
s,
alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
s, and
thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s are tolerated by diimide, but these same groups would typically be degraded by metal catalysts. The reagent preferentially reduces alkynes and unhindered or strained alkenes to the corresponding alkenes and alkanes.


Related

The
dication A dication is any cation, of general formula X2+, formed by the removal of two electrons from a neutral species. Diatomic dications corresponding to stable neutral species (e.g. formed by removal of two electrons from H2) often decay quickly into ...
ic form, HNNH2+ (diprotonated dinitrogen), is calculated to have the strongest known chemical bond. This ion can be thought of as a doubly protonated nitrogen molecule. The
relative bond strength order Relative may refer to: General use * Kinship and family, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are said to be ''relatives'' Philosophy *Relativism, the concept that ...
(RBSO) is 3.38. FNNH2+ and
FNNF Dinitrogen difluoride is a chemical compound with the formula N2F2. It is a gas at room temperature, and was first identified in 1952 as the thermal decomposition product of the azide N3F. It has the structure F−N=N−F and exists in both a ' ...
2+ have slightly lower strength bonds.


References

{{Hydrides by group Azo compounds Nitrogen hydrides Reducing agents Gases with color