Preparation of a Synthetic Indian Yellow
Katherine
Spendel*,
Dr.
M.
Scott
Goodman*,
Dr.
Rebecca
Ploeger
†,
and
Dr.
Aaron
Shugar
†
Contact: Katherine Spendel
SUNY - Buffalo State *Chemistry Department; †Art Conservation Department
[email protected]
Introduction
Indian yellow is a yellow-orange pigment (Fig. 1) often reported as being
extracted from the urine of cows fed only mango leaves (Magnifera
Indica). The production of Indian yellow was banned around 1910 due to
the inhumane nature1. The relative chemical un-reactivity of the
constituents, euxanthone and glucuronic acid (Fig. 2), has made
production of a synthetic version difficult. A new method was developed
to form a synthetic compound that mimics that spectral properties,
including the characteristic fluorescence (Fig. 3) of Indian yellow, by
substituting various surrogate groups at the glucuronic acid binding site.
Euxanthone
B
Glucuronic acid
Figure 1. A solid
orange ball of
Indian
yellow
pigment (Forbes
Collection).
Figure 2. Chemical structure of
Indian Yellow (Euxanthic acid).
Experimental and Synthesis
CH3 I
4-Bromobutyric acid ethyl ester
Step 2a Saponification
of ethyl ester in B
Step 3 Acidification to
generate the free form
acid (pale yellow
precipitate)
1M NaOH
2a
3000
2500
2000
1500
1000
1- MgCl2•6H2O
2- dilute NH4OH
Table 1. XRD peak
positions
of
the
synthesis products from
scheme 1. B, A, and C.
1- MgCl2•6H2O
2- dilute NH4OH
A
Euxanthone with
butyric acid surrogate,
Mg salt
500
0
35000
A
A
30000
25000
20000
15000
10000
5000
0
70000
60000
C
C
50000
40000
30000
20000
10000
Euxanthone no
surrogate,
Mg salt
Figure 6. Formation of three surrogate Indian yellows by forming magnesium salts
of a (A) methylated euxanthone, (B) carboxylated euxanthone, and (C)
unsubstituted euxanthone. Yellow products were photographed under normal (left)
and UVA (right) illumination.
Figure 4. XRD spectra of the
synthesis
products
from
scheme 1. B, A, and C.
UVA Fluorescence
4
Euxanthone with
methyl surrogate,
Mg salt
3500
0
3
1- MgCl2•6H2O
2- dilute NH4OH
B
4000
Dilute HCl
Dilute HCl
Step 4 Formation of
magnesium salt (dark
yellow precipitate)
XRD peak position
Scheme 1
B
A
C
Position Position Position
6.4
7.6
7.7
8.6
9.4
10.3
10.5
11.6
12.6
12.4
12.6
15.2
18.3
18.6
18.6
19.7
21.5
21.1
21.1
21.7
22.4
23.8
23.9
23.9
24.7
25.2
24.6
26.0
26.5
27.6
27.5
28.9
28.6
29.3
31.3
29.5
30.7
31.1
33.0
33.9
33.7
35.9
35.2
36.6
38.0
37.7
38.5
40.5
41.9
44.9
44.9
45.6
47.3
49.1
48.1
50.8
52.5
56.8
7.72
10.62
13.52
16.42
19.32
22.22
25.12
28.02
30.92
33.82
36.72
39.62
42.52
45.42
48.32
51.22
54.12
57.02
59.92
62.82
K2CO3 in DMF
B
4500
7.76
10.7
13.64
16.58
19.52
22.46
25.4
28.34
31.28
34.22
37.16
40.1
43.04
45.98
48.92
51.86
54.8
57.74
60.68
63.62
1
Step 2 – Addition of
surrogate groups: A:
methyl iodide; B: 4Bromobutyric acid ethyl
ester
2
C
B
µ-FTIR and Raman
XRD
5.86
6.9
7.94
8.98
10.02
11.06
12.1
13.14
14.18
15.22
16.26
17.3
18.34
19.38
20.42
21.46
22.5
23.54
24.58
25.62
26.66
27.7
28.74
29.78
30.82
31.86
32.9
Scheme 1. A, B, C: Synthesis of euxanthone based
magnesium salts
A
Figure 3. Photographs of a watercolour
pigment book under normal (a) and
UVA (b) illumination illustrating the
fluorescence characteristics.
Results
Euxanthone and the various surrogate groups were reacted
together followed the reaction schemes 1 (A,B,C). Characterization
was performed with µ-FTIR (Thermo, Contiuum), Raman
spectroscopy (Bruker, Senterra), XRD (Bruker, D8 Venture), py-GCMS (Frontier 2020 pyrolyzer, GC-MS Agilent). Samples were
exposed to UVA radiation for imaging. Results for the µ-FTIR,
Raman Spectroscopy and XRD will be discussed here.
Step 1 – Deprotonation
of euxanthone (red
solution)
A
B
C
Conclusion
To this point, synthesis of Indian yellow substitutes have produced precipitates of
similar colour and fluorescence to known Indian yellow. Characterization is ongoing,
and will be compared to the Forbes collection and Winsor & Newton late 19th
century watercolour paint-outs. Further investigation will be done on the wavelength
of fluorescence of the surrogates compared authentic Indian yellow.
Figure 5. µ-FTIR (blue) and Raman (red)
spectra of the synthesis products from
scheme 1. B, A, and C.
Table 2. Origin of the peaks in the FTIR and Raman spectra of
the products of schemes B, A, and C.
Origin
OH
Symmetric CH2 stretch
C=O (ketone)
Aromatic
Ether
C=C stretch
Ring stretch
Ring vibrations
Ring breathing
Ring deformation
FTIR
3500-2962, 1149
2962*
1619
1588, 1108, 719, 697
1270*, 1233
-
Raman
2913**
1631
1546
1421*, 1370*
1234
1168*, 988*, 694
514*
*Slight variation between samples; ** Not observed in Scheme A
References
1) Feller, R. L., Roy, A., FitzHugh, E. W., & Berrie, B. H. (1986). Artists' pigments: A
handbook of their history and characteristics. Washington: National Gallery of Art.
Acknowledgements
Dr. A. Nazarenko, K. Harada, Dr. N. Khandekar