Preparation of a Synthetic Indian

Contact: Katherine Spendel Katherine Spendel*, Dr. M. Scott Goodman*, Dr. Rebecca Ploeger †, and Dr. Aaron Shugar † [email protected] SUNY - Buffalo State *Chemistry Department; †Art Conservation Department Introduction Euxanthone Indian yellow is a yellow-orange (Fig. 1) often reported as being A 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 B constituents, euxanthone and glucuronic acid (Fig. 2), has made production of a synthetic version difficult. A new method was developed Glucuronic acid to form a synthetic compound that mimics that spectral properties, Figure 1. A solid orange ball of Figure 3. Photographs of a watercolour including the characteristic fluorescence (Fig. 3) of Indian yellow, by Indian yellow Figure 2. Chemical structure of pigment book under normal (a) and substituting various surrogate groups at the glucuronic acid binding site. pigment (Forbes Indian Yellow (Euxanthic acid). UVA (b) illumination illustrating the Collection). fluorescence characteristics. Experimental and Synthesis Results Euxanthone and the various surrogate groups were reacted XRD µ-FTIR and Raman together followed the reaction schemes 1 (A,B,C). Characterization 4500 XRD peak position B was performed with µ-FTIR (Thermo, Contiuum), Raman 4000 B Scheme 1 spectroscopy (Bruker, Senterra), XRD (Bruker, D8 Venture), py-GC- B A C 3500 MS (Frontier 2020 pyrolyzer, GC-MS Agilent). Samples were Position Position Position 3000 6.4 2500 exposed to UVA radiation for imaging. Results for the µ-FTIR, 7.6 7.7 2000 Raman Spectroscopy and XRD will be discussed here. 8.6 9.4 10.3 10.5 1500 11.6 1000 Scheme 1. A, B, C: Synthesis of euxanthone based 12.6 12.4 12.6 Step 1 – Deprotonation 500 magnesium salts 15.2 of euxanthone ( 0

18.3 18.6 18.6 6.9

5.86 7.94 8.98 12.1 17.3 22.5 27.7 32.9

11.06 13.14 14.18 15.22 16.26 18.34 19.38 20.42 21.46 23.54 24.58 25.62 26.66 28.74 29.78 30.82 31.86 solution) 19.7 10.02 35000 B C 21.5 21.1 21.1 A A 21.7 30000 A 22.4 25000 23.8 23.9 23.9 24.7 25.2 24.6 20000 26.0 K CO in DMF 15000 1 2 3 26.5 27.6 27.5 28.9 28.6 10000 29.3 31.3 29.5 Step 2 – Addition of 5000 30.7 surrogate groups: A: 31.1 0 methyl iodide; B: 4- 33.0

CH3 I 7.72

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 Bromobutyric acid ethyl 4-Bromobutyric acid ethyl ester 33.9 33.7 10.62 70000 ester 2 35.9 35.2 36.6 60000 C C Step 2a Saponification 38.0 37.7 38.5 50000 of ethyl ester in B 1M NaOH 40.5 41.9 40000 44.9 44.9 Step 3 Acidification to 45.6 30000 generate the free form 2a 47.3 20000 acid (pale yellow 49.1 48.1 precipitate) 50.8 52.5 10000 56.8 0

Dilute HCl Dilute HCl

7.76 10.7 25.4 40.1 54.8

16.58 19.52 22.46 28.34 31.28 34.22 37.16 43.04 45.98 48.92 51.86 57.74 60.68 63.62 Table 1. XRD peak 13.64 3 positions of the Figure 4. XRD spectra of the synthesis products from synthesis products from Figure 5. µ-FTIR () and Raman (red) 1- MgCl •6H O 2 2 scheme 1. B, A, and C. scheme 1. B, A, and C. spectra of the synthesis products from 1- MgCl •6H O 2- dilute NH OH 2 2 4 scheme 1. B, A, and C. 2- dilute NH4OH 1- MgCl2•6H2O Step 4 Formation of 2- dilute NH4OH Table 2. Origin of the peaks in the FTIR and Raman spectra of magnesium salt (dark UVA Fluorescence the products of schemes B, A, and C. yellow precipitate) 4 Origin FTIR Raman A OH 3500-2962, 1149 -

Symmetric CH2 stretch 2962* 2913** C=O (ketone) 1619 1631 Euxanthone with Euxanthone with Euxanthone no methyl surrogate, butyric acid surrogate, surrogate, Aromatic 1588, 1108, 719, 697 - Mg salt Mg salt Mg salt B Ether 1270*, 1233 - C=C stretch - 1546 Ring stretch - 1421*, 1370* Figure 6. Formation of three surrogate Indian by forming magnesium salts Ring vibrations - 1234 Ring breathing - 1168*, 988*, 694 of a (A) methylated euxanthone, (B) carboxylated euxanthone, and (C) C unsubstituted euxanthone. Yellow products were photographed under normal (left) Ring deformation - 514* and UVA (right) illumination. *Slight variation between samples; ** Not observed in Scheme A

Conclusion References To this point, synthesis of Indian yellow substitutes have produced precipitates of 1) Feller, R. L., Roy, A., FitzHugh, E. W., & Berrie, B. H. (1986). Artists' : A handbook of their history and characteristics. Washington: National Gallery of Art. similar colour and fluorescence to known Indian yellow. Characterization is ongoing, and will be compared to the Forbes collection and Winsor & Newton late 19th Acknowledgements century watercolour paint-outs. Further investigation will be done on the wavelength of fluorescence of the surrogates compared authentic Indian yellow. Dr. A. Nazarenko, K. Harada, Dr. N. Khandekar