Series editors' preface - Wood Tools

512 Conservation of Furniture
group is also called an amino group). The
exposed lone pair of electrons on the nitrogen
makes them moderately polar. Amines are classified
as primary, secondary or tertiary, depending
on the number of organic groups that are
attached to the nitrogen atom. Primary and
secondary amines can form strong hydrogen
bonds. Tertiary amines do not hydrogen-bond
within themselves but do form hydrogen-bonds
with water or other hydroxylic solvents. Amines
are relatively weak bases and are sometimes
used to combine solvent and reagent action to
break down oil/resin films. Amines generally
have a low vapour pressure and require a rinse
procedure to remove residues. As bases, they
have the potential to saponify fatty, oily or
greasy materials. They should be used with care
on pH-sensitive surfaces.
H
|
R – N – H
Amine functional group
OH
|
CH2 |
CH2 |
OH – CH2 – CH2 – N – CH2 – CH2 – OH
Triethanolamine
In conservation, triethanolamine is often
referred to as TEA. It should be noted that in
the broader world of organic chemistry, TEA
is shorthand for triethylamine. These two
solvents have different properties and are not
interchangeable.
Cyclic amines All classes of solvents can have
cyclic structures. Benzene rings that have an
amino (NH 2) group attached are called
arylamines. Heterocyclic amines contain one or
more nitrogen atoms within the cyclic structure.
N
|
CH3 O
N-methyl-2-pyrrolidinone
N-methyl-2-pyrrolidinone is a heterocyclic
amine. The N indicates that the methyl group
is attached to the nitrogen atom. N-methyl-2-
pyrrolidone has a marked swelling action on
oil-based varnishes and paint and is therefore
sometimes used to remove oil based retouching.
N-methyl-2-pyrrolidone is also an effective
solvent for polysaccharides (Horie, 1992).
O
N
Morpholine has both oxygen and nitrogen
atoms substituted within the cyclic structure. It
is an effective solvent for shellac, casein and
linseed oil, all of which are sensitive to
elevated pH. It has an unpleasant odour and
with an OES LTEL of 20 ppm, it is not recommended
for general use.
Amides
O O O O
C–N R–C–N–H 2 R–C–N(H,R 1) R–C–N(R 1,R 2)
Amides contain a C⎯N group, as shown in
the examples above, where R, R 1 and R 2 represent
different alkyl groups. The lone pairs on
the oxygen and nitrogen make amides very
polar, although amides are essentially neutral
in terms of acid/base reactions. Examples of
amides are:
O
| |
CH3 – C – NH2 Acetamide
O
| |
CH3 – C – NH – CH3 N-methylacetamide
O
||
H – C – N
CH 3
CH 3
Dimethyl formamide
morpholine
Dimethyl formamide has been used for removing
soot from water gilding but will swell oilbased
layers. It is too harmful for general use.
11.3.2 Physical properties of solvents
A wide range of organic solvents with finely
graded properties is available from chemical