Transcript Chapter 7 - Wits Structural Chemistry

CHEM 2017
2008
lect 5 + 6
Hydrogen Peroxide etc.
HYDROGEN PEROXIDE
HYDROGEN PEROXIDE
Inorganic peroxy compounds
H2O2
Discovered 1818.
Action of nitric acid on barium
peroxide
Difficult reaction – low peroxide
concentration - low stability
1878 Electrolysis dilute sulphuric acid
1908 Commercial electrolysis plants
AO PROCESS
Substantial improvements introduced
in the AO Process
Basic organic chemistry established
in1930s
Commercial plants established 1953
(Du Pont)
Separation of reduction and oxidation
stages
Hydrogen peroxide separated from
working solution using liquid-liquid
extraction
Working solution is organic / use
water as extracting phase
AO PROCESS
Quinones soluble in non-polar
solvents [BENZENE, TOLUENE,
ALKYLBENZENES]
Hydroquinones soluble in polar
solvents [VARIOUS ESTERS,
NONYL ALCOHOLS]
In practice use mixed solvent system
AO PROCESS - PROBLEMS
Tetra problem – too much
hydrogenation
AO PROCESS - PROBLEMS
Tetra problem – too much hydrogenation
Oxidation step is too slow
Working solution “diluted” by less reactive
intermediates
Problem best addressed by careful choice of
hydrogenation catalysts
Otherwise have to reverse the over-hydrogenation
by exposing working solution to hydrogen
acceptors e.g. alkenes in the presence of a
catalyst (alumina) - THIS INTERUPTS THE
PROCESS
AO PROCESS - PROBLEMS
Epoxide formation - does not take
part in hydrogenation/oxidation cycle
– wasted quinone
React epoxide with tetra compound
can provide a solution
AO PROCESSHYDROGENATION STAGE
Ni catalysts e.g. Raney Ni
Ni catalysts are pyrophoric
Ni leads to tetra compound
Pd catalysts now preferred (more
expensive, but overall better performance)
Catalyst separation must be 100%
AO PROCESS – OXIDATION
STAGE
Exposure of hydroquinone to air
Hydrogen peroxide formed in a noncatalytic step
15-30% aq. solution possible
Purification (remove traces of solvents)
Stabilization after concentration to 50-70%
Stored/used
ALTERNATIVE PROCESSES
Electrolysis still being improved but
not widely used
Shell: Oxidation of alcohols
ALTERNATIVE PROCESSES
Electrolysis still being improved but
not widely used
Shell: Oxidation of alcohols
Direct hydrogen oxidation – highly
desirable process but “difficult” RECENT PROMISE INVOLVING Au
CATALYSTS. Concept: Use of
hydrogen peroxide in situ
Au CATALYSIS
e.g. Propene + HYDROGEN +
OXYGEN  PROPYLENE OXIDE
Hydrogen peroxide oxidises the
propene as it is formed
Still in development
CHEMICAL PROPERTIES
Weak acid
Oxidizing agent
Reducing agent
MOST COMMERCIAL
APPLICATIONS RELY ON STRONG
OXIDATION PROPERTIES
APPLICATIONS AND CHEMISTRY
BLEACHING (AVOIDS USE OF
CHLORINE)
ANTISEPTIC
ENVIRONMENTAL – DESTRUCTION
OF CYANIDE (MINING) AND
SULPHITES AND IN SEWAGE
SLUDGE TREATMENT (SUDDEN
OXYGEN BOOST)
PERBORATES
Source of hydrogen peroxide
Used in detergents
Effective at 90C unless activators are used
as well. Widely adopted in Europe
Less important in USA (cold water washing
– 55C) historically and chlorine containing
bleaches preferred – but now that
activators are available perborate use
being considered