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The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 22
(2017) pp 137-141
An Improved Laboratory Synthesis of Betaine-30: A Solvatochromic Dye
Magrieta Snyman and Brian P. Rempel*
Department of Science, Augustana Campus, University of Alberta 4901-46th Ave. Camrose, Alberta, T4V 2R3 Canada, brempel@ualberta.ca
Received June 2, 2017. Accepted July 27, 2017.
Published: 11 August 2017
Abstract. Empirical
solvent polarity can be measured with betaine-30, a highly solvatochromatic
compound meaning that solutions of betaine-30 in different solvents are
different colors in response to the polarity of the solvent. These solutions
are excellent tools to visualize solvent polarity, a concept that underlies the
important role solvent plays in a chemical reaction or process. By showing how
the solution color changes with solvent polarity, students can draw an analogy with
non-visible properties that also depend on solvent polarity such as reaction
rates. The synthesis of betaine-30 is a straightforward four-step convergent
synthesis starting from inexpensive starting materials: 1,3-diphenylpropenone
(chalcone), acetophenone and 2,6-diphenylphenol. Herein, an updated and
improved synthesis of betaine-30 is presented that is quick, easy,
high-yielding, and can be readily accomplished by senior undergraduate organic
chemistry students. In particular, a better method for preparation of the first
intermediate, 2,4,6-triphenylpyrylium hydrogen sulfate from acetophenone and
1,3-diphenylpropenone (chalcone), is described. As well, nitrosylation of
2,6-diphenylphenol followed by reduction with sodium dithionite produces
4-amino-2,6-diphenylphenol in an efficient reaction sequence. Finally, the
greater purity of the intermediates leads to a higher yield for the final
coupling to form pure betaine-30.
Key Words: Laboratories and Demonstrations; organic chemistry; laboratory instruction; organic synthesis; solvent and solvent effects; UV-Vis spectroscopy; solvatochromism
(*) Corresponding author. (E-mail: brempel@ualberta.ca)
Article in PDF format (103 KB) HTML format
Supporting Materials:
Complete experimental details, LC-MS analysis of student products, student handouts, evaluative material, sample anonymized student laboratory reports. (8670 KB)
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