equation, pV = nRT, where n is the
amount of gas in the specimen and R
is the *gas constant. The gas laws
were Ürst established experimentally
for real gases, although they are
obeyed by real gases to only a limited
extent; they are obeyed best at high
temperatures and low pressures. See
also equation of state.
gasohol A mixture of petrol (gasoline) and alcohol (i.e. typically
ethanol at 10%, or methanol at 3%),
used as an alternative fuel for cars
and other vehicles in many countries. The ethanol is obtained as a
*biofuel by fermentation of agricultural crops or crop residues, for example sugar cane waste. Many cars
can also use a mixture of 85% ethanol
and 15% petrol, called E85. Ethanolbased gasohol has a higher octane
rating and burns more completely
than conventional petrol, thus lowering some emissions. However, the
ethanol can damage certain engine
components, such as rubber seals.
Methanol-based gasohol is more toxic
and corrosive, and its emissions include formaldehyde, a known carcinogen.
gas oil A high-density petroleum
fraction (between kerosene and lubricating oil), whose molecules have up
to 25 carbon atoms. It is used as a domestic and industrial heating fuel.
gasoline See petroleum.
gas-phase electrophoresis See
ion-mobility spectrometry.
gas thermometer A device for
measuring temperature in which the
working Ûuid is a gas. It provides the
most accurate method of measuring
temperatures in the range 2.5 to
1337 K. Using a Üxed mass of gas a
constant-volume thermometer measures the pressure of a Üxed volume
of gas at relevant temperatures, usually by means of a mercury manometer and a barometer.
Gattermann–Koch reaction A reaction of the type C 6 H 6 → C 6 H 5 CHO,
used to introduce aldehyde groups
onto benzene rings. It is used in the
industrial manufacture of benzaldehyde. A mixture of hydrogen chloride and carbon monoxide is passed
through benzene using a Lewis acid
such as aluminium chloride as a catalyst. An intermediate H–CϵOC
+ is
formed and electrophilic substitution
takes place on the benzene ring.
There is a variation of the reaction,
sometimes simply called the Gattermann reaction, in which the –CHO
group is substituted onto the benzene ring of a phenol. In this reaction hydrogen cyanide is used rather
than carbon monoxide. A mixture of
zinc cyanide and hydrochloric acid
produces the hydrogen cyanide along
with zinc chloride to act as the catalyst. The electrophile is HCNH
+
which produces an imine intermediate
C 6 H 5 OH → HOC 6 H 4 CH=NH
This then hydrolyses to the aldehyde
HOC 6 H 4 CHO. If an organic cyanide
(nitrite) RCN is used, a ketone is produced. The reaction was discovered
by Ludwig Gattermann and J.C. Koch
in 1897. The use of hydrogen cyanide
was reported by Gattermann in 1907.
Gattermann reaction A variation
of the *Sandmeyer reaction for
preparing chloro- or bromoarenes by
reaction of the diazonium compound. In the Gattermann reaction
the aromatic amine is added to
sodium nitrite and the halogen acid
(10°C), then fresh copper powder
(e.g. from Zn + CuSO 4 ) is added and
the solution warmed. The diazonium
salt then forms the haloarene, e.g.
C 6 H 5 N 2
+
Cl
–
→ C 6 H 5 Cl + N 2
The copper acts as a catalyst. The re243
Gattermann reaction
g
www.AzShimi.ir www.AzShimi.com
amount of gas in the specimen and R
is the *gas constant. The gas laws
were Ürst established experimentally
for real gases, although they are
obeyed by real gases to only a limited
extent; they are obeyed best at high
temperatures and low pressures. See
also equation of state.
gasohol A mixture of petrol (gasoline) and alcohol (i.e. typically
ethanol at 10%, or methanol at 3%),
used as an alternative fuel for cars
and other vehicles in many countries. The ethanol is obtained as a
*biofuel by fermentation of agricultural crops or crop residues, for example sugar cane waste. Many cars
can also use a mixture of 85% ethanol
and 15% petrol, called E85. Ethanolbased gasohol has a higher octane
rating and burns more completely
than conventional petrol, thus lowering some emissions. However, the
ethanol can damage certain engine
components, such as rubber seals.
Methanol-based gasohol is more toxic
and corrosive, and its emissions include formaldehyde, a known carcinogen.
gas oil A high-density petroleum
fraction (between kerosene and lubricating oil), whose molecules have up
to 25 carbon atoms. It is used as a domestic and industrial heating fuel.
gasoline See petroleum.
gas-phase electrophoresis See
ion-mobility spectrometry.
gas thermometer A device for
measuring temperature in which the
working Ûuid is a gas. It provides the
most accurate method of measuring
temperatures in the range 2.5 to
1337 K. Using a Üxed mass of gas a
constant-volume thermometer measures the pressure of a Üxed volume
of gas at relevant temperatures, usually by means of a mercury manometer and a barometer.
Gattermann–Koch reaction A reaction of the type C 6 H 6 → C 6 H 5 CHO,
used to introduce aldehyde groups
onto benzene rings. It is used in the
industrial manufacture of benzaldehyde. A mixture of hydrogen chloride and carbon monoxide is passed
through benzene using a Lewis acid
such as aluminium chloride as a catalyst. An intermediate H–CϵOC
+ is
formed and electrophilic substitution
takes place on the benzene ring.
There is a variation of the reaction,
sometimes simply called the Gattermann reaction, in which the –CHO
group is substituted onto the benzene ring of a phenol. In this reaction hydrogen cyanide is used rather
than carbon monoxide. A mixture of
zinc cyanide and hydrochloric acid
produces the hydrogen cyanide along
with zinc chloride to act as the catalyst. The electrophile is HCNH
+
which produces an imine intermediate
C 6 H 5 OH → HOC 6 H 4 CH=NH
This then hydrolyses to the aldehyde
HOC 6 H 4 CHO. If an organic cyanide
(nitrite) RCN is used, a ketone is produced. The reaction was discovered
by Ludwig Gattermann and J.C. Koch
in 1897. The use of hydrogen cyanide
was reported by Gattermann in 1907.
Gattermann reaction A variation
of the *Sandmeyer reaction for
preparing chloro- or bromoarenes by
reaction of the diazonium compound. In the Gattermann reaction
the aromatic amine is added to
sodium nitrite and the halogen acid
(10°C), then fresh copper powder
(e.g. from Zn + CuSO 4 ) is added and
the solution warmed. The diazonium
salt then forms the haloarene, e.g.
C 6 H 5 N 2
+
Cl
–
→ C 6 H 5 Cl + N 2
The copper acts as a catalyst. The re243
Gattermann reaction
g
www.AzShimi.ir www.AzShimi.com