Agua

Laboratory Experiment
pubs.acs.org/jchemeduc

Detection of Salicylic Acid in Willow Bark: An Addition to a Classic
Series of Experiments in the Introductory Organic Chemistry
Laboratory
Matthew D. Clay* and Eric J. McLeod
Department of Chemistry, St. Mary’s University College, Calgary, AB, Canada, T2X 1Z4
S
* Supporting Information

ABSTRACT: Salicylic acid and its derivative,acetylsalicylic acid, are often
encountered in introductory organic chemistry experiments, and mention is
often made that salicylic acid was originally isolated from the bark of the
willow tree. This biological connection, however, is typically not further
pursued, leaving students with an impression that biology and chemistry are
separate entities in the laboratory. We have developed a laboratorythat
investigates this biological connection in which salicylic acid is extracted from
willow bark and detected using thin-layer chromatography. This experiment
can be adopted as either a standalone experiment or integrated into other
laboratory courses with current experiments involving salicylic acid.
KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate,Interdisciplinary/Multidisciplinary,
Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Drugs/Pharmaceuticals, Natural Products,
Thin Layer Chromatography

T

he widespread use of acetylsalicylic acid (Aspirin) and its
relatively simple structure make it an attractive synthetic
target in the introductory organic chemistry laboratory, and a
number of effective syntheses forundergraduate laboratories
have been developed.1 Many laboratory courses also include an
experiment wherein thin-layer chromatography (TLC) is used
to assess the purity of the synthesized acetylsalicylic acid and to
analyze the composition of various commercial analgesic
preparations.2,3 In both experiments, the introductory matter
often includes a discussion of the history of salicylic acid,
focusingon the use of willow bark in native medicine to relieve
fever and pain and the subsequent discovery that the
therapeutic properties of the bark were due to salicylic acid.
The biological connection of acetylsalicylic acid to willow
bark, however, is not further pursued experimentally, which
likely reinforces the mistaken belief held by students that
biology and chemistry are separateentities,4 particularly within
the laboratory. Not only may this misconception be detrimental
to those students entering an increasingly multidisciplinary
scientific community,5 but those students whose interests lie in
biology (for which organic chemistry is often a required course)
may be missing some of the important connections to their
discipline that could serve to motivate them and improvetheir
view on the relevance of the course.
We have developed an experiment for the introductory
organic chemistry laboratory in which salicylic acid is extracted
from willow bark and detected using TLC. This experiment can
be run by itself in one 3-h laboratory session or easily integrated
into the classic experimental sequences involving salicylic acid
© XXXX American Chemical Society andDivision of Chemical Education, Inc.

referenced above. Students are introduced to the common
experimental techniques of extraction, TLC, and the use of a
reflux apparatus, while the modern reality that the chemical
laboratory is highly interdisciplinary is reinforced.
The detection of salicylic acid in willow bark is not a novel
idea. The rising popularity of willow bark extract as analternative therapeutic to acetylsalicylic acid has led to the
development of many effective methods for the detection and
quantification of salicylic acid and its derivatives in willow
bark.6,7 However, the techniques used are not suitable or easily
adapted to the introductory organic chemistry laboratory,
necessitating the development of a method for the rapid
extraction and detection of...