172.5–174 °C). Microanalysis found C, 80.5; H, 6.1; N, 5.0%
10.15% (C H N O requires C, 75.52; H, 6.58; N, 10.16%).
26 27 3 2
(C H O N requires C, 80.5; H, 6.0; N, 4.9%). DSC and
DSC indicated reasonable purity, analysis revealing a small
38 34 3
2
TLC (alumina, 951 toluene–ethyl acetate) indicated purity,
showing a sharp endotherm at 172.3 °C and a single dark
green spot respectively. FTIR (KBr)/cm−1: 1752 (lactone
CLO).
endotherm at 248.4 °C and a sharp, major endotherm at
261.7 °C, with decomposition occurring at around 316 °C. TLC
(alumina, 951 toluene–ethyl acetate) revealed a single green
spot of R 0.57. FTIR (KBr)/cm−1: 1752 (lactone CLO).
f
Vinylphthalide colour former 3. Magnesium (98%, 4.2 g,
0.17 mol) and diethyl ether (20 ml) were stirred under nitrogen
as iodomethane (99%, 25.0 g, 0.17 mol) was added dropwise
over 20 min at such a rate as to maintain a continuous
exotherm and gentle refluxing. The mixture was gently refluxed
for 25 min by which time almost all of the magnesium had
dissolved. The reaction mixture was protected from light and
a solution of Michler’s ketone (98%, 9.0 g, 33 mmol) in toluene
(280 ml) at room temperature was run in. The mixture was
stirred under nitrogen in the absence of light at ambient
temperature for 22 h, before cautiously quenching with water
(200 ml) to give a light blue emulsion, which was stirred for
15 min. A solution of ammonium chloride (30 g) and acetic
acid (99%, 15 ml) in water (150 ml) was added and the whole
stirred for 3.5 h. The aqueous phase was washed twice with
toluene (50 ml) and the extracts combined with the organic
phase, from which the solvent was removed by rotary evapor-
ation after drying overnight with magnesium sulfate. The pale
blue-green residue (8.59 g, 98% crude yield, mp 116–120 °C)
was recrystallised in ethanol, furnishing Michler’s ethylene (8)
as a pale blue lustrous solid (7.15 g, mp 121–123 °C, lit.,18
121–122 °C).
Developers 6a–h. Apart from the readily available 6a, the
developers 6 were synthesised from 4-aminophenol by the
methods of Fierz-David and Kuster.20 The 4-propionyl ana-
logue 6b was obtained using propionic anhydride, whereas the
longer alkyl chain derivatives (R=C H to C H ) were
synthesised from the corresponding acid chlorides, while the
stearoyl derivative 6h was prepared by condensation with
stearic acid.
3
7
7 15
Preparation of the compositions
Formulations of 5051:1 stearic acid (2.00 g), developer 6
(Table 3) and 1 (0.040 g) were prepared by heating the mixture
to 100–105 °C and stirring until dissolution was complete, or
until no more dissolution occurred, and quenching with the
addition of ca. 20 ml of cold water. The solidified wax was
filtered off, allowed to air-dry overnight and powdered.
Series of compositions of ratio 255151 and 1005151 were
also prepared in a similar manner. Formulations containing 2
(255151), 3 (505251) and 4 (505251) were made by the same
procedure, except that the mixtures were heated to 95–100 °C,
105–110 °C and 100–105 °C, respectively. The ratios strictly
only apply to compositions containing 6a; the amounts of
developer listed in Table 3 are equimolar so that, within a
particular series of compositions, each member of the range
consists of a fixed molar ratio of developer to colour former
and co-solvent.
The procedure for measuring the reflectance of the powdered
formulations involved packing the material into a glass-fronted
cylindrical cell comprising two close-fitting components. The
composition was compressed in the cell by insertion of the
cylinder and the reflectance measured (scan speed
240 nm min−1); the powder was displaced and re-compressed
before taking a second measurement. The technique was found
to yield consistent results.
A mixture of 8 (1.33 g, 5.0 mmol), 2-(4-N,N-dimethylamino-
benzoyl)-3,4,5,6-tetrachlorobenzoic
acid
919
(2.04 g,
5.0 mmol) and acetic anhydride (7.5 ml) was stirred and
heated to reflux for 20 min. The dark green mixture was
allowed to cool and poured into a mixture of toluene (50 ml),
ice (50 ml) and aqueous ammonia (32%, 10 ml). The emulsion
was destroyed by addition of a little dichloromethane; the
organic phase was collected and the aqueous phase extracted
with more dichloromethane. The combined extracts were
washed several times with water, dried (magnesium sulfate)
and rotary evaporated to dryness, giving a dark yellow-
brown solid (2.94 g, 90% crude yield, mp 220–222 °C).
Recrystallisation (methoxyethanol, methoxyethanol–DMF
1251 twice) furnished 3 as green needle-like crystals (1.03 g,
mp 227.5–229 °C), which darken in sunlight, but return to
their original colour in the dark. Microanalysis found C, 61.9;
H, 4.8; N, 6.1; Cl, 20.8% (C H N O Cl requires C, 62.3; H,
Molecular modelling
34 31 3 2
4
4.8; N, 6.4; Cl, 21.6%). DSC indicated reasonable purity,
showing a single endotherm at 226.6 °C. TLC (alumina, 951
toluene–ethyl acetate) revealed one blue-green spot. FTIR
(KBr)/cm−1: 1758 (lactone CLO).
The ‘Hyperchem’ software package (Release 3 For Windows,
Autodesk Inc.) was used in an attempt to visualise the geometry
of the ring-opened colour former molecules. The procedure
involved optimising the geometry by using molecular mechan-
ical methods, conducting the iterative energy-minimising rou-
Fluorene colour former 4. Aluminium chloride (96%, 50.0 g,
0.36 mol), urea (7.5 g, 0.12 mol) and aluminium chloride
hexahydrate (99%, 0.75 g, 3.1 mmol) were stirred and heated
to 125 °C. Crystal Violet Lactone (1) (97%, 5.2 g, 12 mmol)
was added and the mixture stirred at 135–140 °C for 4 h.
Heating was continued for another 18 h by which time the
reaction mixture had become a solid mass. The reaction was
quenched by gradual addition of water (400 ml) to give a
blue-green suspension, which was treated with hydrogen per-
oxide (30%, 1.2 ml) and stirred for 1.5 h. The suspension was
extracted several times with dichloromethane; the combined
extracts were washed and dried over magnesium sulfate.
Removal of the drying agent and solvent furnished a dull
green solid (4.43 g, 89% crude yield). Three recrystallisations
˚
tines to the desired energy gradient (0.01 kcal A−1 mol−1)
with the Polak–Ribiere algorithm. The MM+ force field was
used as it was deemed the most appropriate for relatively
small molecules like the colour formers. For the sake of
simplicity, the colour formers were assumed to ring open to
give a free carboxylic acid group, i.e. the nature of the
developer and the type of association was not considered in
the modelling.
Table 3 Masses of developers 6 used in 505151 compositions
Developer
Mass/g
Developer
Mass/g
(toluene/charcoal) gave
4 as buff crystals (1.20 g, mp
6a
6b
6c
6d
0.0400 0.0004
0.0438 0.0004
0.0475 0.0004
0.0512 0.0005
6e
6f
6g
6h
0.0549 0.0005
0.0586 0.0005
0.0623 0.0005
0.0995 0.0005
225–227.5 °C). Repeated recrystallisation of 0.40 g of this
material from toluene and ethanol afforded analytically-pure
pale cream crystals (0.07 g, mp 237–242 °C, lit.,8 244–246 °C,
lit.,10 240–245 °C). Microanalysis found C, 75.3; H, 6.7; N,
2682
J. Mater. Chem., 1998, 8, 2677–2683