Synthesis and Characterization of Dibenzalacetone

Synthesis and Characterization of Dibenzalacetone Tan Yong Jie (m15604 Synthesis and Characterization Characterization of Dibenzalacetone Dibenzalacetone Aim: Aim: The aim of this experiment is to prepare a sample of dibenzalacetone (via a reaction of acetone with benzaldehyde) and determine its yield. The purity of the product will be determined usin a meltin point apparatus and T!C will also be conducted to determine if there is contamination contamination from reactants. Intro Introdu duct ctio ion n "enzal "enzaldeh dehyd yde# e# a primar primary y compo componen nentt of bitte bitterr almon almond d oil# oil# has has a characteristic pleasant almond$li%e odor. "enzaldehyde can also be obtained from other natural sources such as from almonds# apricots# apples and cherry %ernels# which contain sinificant amounts of amydalin# a lycoside that brea%s down under  enzyme enzyme catalysi catalysis s into benzalde benzaldehyde hyde ( 1). &otably &otably on oxidation oxidation## benzalde benzaldehyde hyde is converted into an odourless benzoic acid# which is a common impurity in laboratory samples (1 (1).  'cetone is a colourless# volatile# flammable liuid that is the simplest %etone. t is miscible with water and serves as an important solvent for cleanin purposes in the laboratory. t is also an important component of nail polish removers as well as paint thinners (2  (2 ). ). Dibenzyl Dibenzyliden ideneace eacetone tone is used as a sunscreen sunscreen compone component nt and as a liand in oranometallic chemistry. t is a briht$yellow solid insoluble in water# but soluble in ethanol. Sunliht causes the compound to be converted to a cyclobutane mixture in a *+,+* +,+- cycloaddition (3 (3). Suction filtration is a method used to remove solvent from solid crystals by the application of reduced pressure in the "chner flas% ( 3). This method offers more control over the rate of filtration compared to ravity filtration. n this experiment suction filtration was used to remove the solvent from the crude product as well as the final product (3 ( 3). /ecrystallization is a purification techniue that exploits the differential solubility of  compounds in solvents of different temperatures. ' near minimum of hot solvent is added to the crude product to dissolve it and then the mixture is allowed to cool slow slowly ly to room room temp temper erat atur ure e (4). (4). 's the tempe temperat ratur ure e decre decrease ases# s# the compou compound nd becomes less soluble and as the solution becomes saturated with the compound it crystalli crystallizes zes out of the solution. solution. Since crystalli crystallizatio zation n is a very thermody thermodynami namically cally selective selective process process that excludes excludes forein particles# particles# the compound compound obtained obtained will will be pure. ' minimum of ice cold solvent is then applied to remove any impurities on the surface (4). Thin$layer chromatoraphy (T!C) is a chromatoraphy techniue used to separate non$volatile mixtures. n a lab settin# T!C can be used to determine the number of  components in a mixture# verify a substance0s identity or monitor the proress of a reaction (5  (5 ). ). T!C has wide applications includin analysis of ceramides and fatty acids# detection of pesticides or insecticides in food and water# analysin the dye comp compos osit itio ion n of fibe fibers rs in fore forens nsic ics# s# assa assayi yin n the the radi radioc oche hemi mica call puri purity ty of  radiopharmaceuticals# radiopharmaceuticals# or identification of medicinal plants and their constituents ( 5 ). ). The stationary phase used in this experiment is silica el coated on aluminium# a polar absorbent. 1n a molecular level# molecules are continuously movin bac% and forth between the free and absorbed states in a dynamic euilibrium euilibrium that depends on three three factor factors# s# namel namely y the polarit polarity y and and size size of the molecu molecule le## the polarity polarity of the stationary phase and the polarity of the solvent. Since silica is polar# more polar  molecules will be more stronly attracted to the stationary phase. The two solvents

1

Synthesis and Characterization of Dibenzalacetone Tan Yong Jie (m15604 used in this experiment# hexane and ethyl acetate# are non$polar and wea%ly polar  respectively. Mechanism:

Procedure: "enzaldehyde (2.2345mol# +.2 ml) and acetone (2.2324 mol# 2.6ml) was added to a 322ml 322ml conic conical al flas%. flas%. &a17 &a17 (2.28 (2.2822m 22mol# ol# +.2) +.2) pelle pellets ts were were placed placed in ethan ethanol ol (2.99mol# +2 ml) and D water (+2 ml) and mixed well in a 322ml conical flas%. This solution was then added to the mixture of benzaldehyde and acetone and swirled continuously for 38 minutes. The product was then collected from the filter paper by sucti suction on filt filtra rati tion on usin usin  D wate waterr as poor poor solv solven ent. t. The The crud crude e prod produc uctt was was re$ re$ crystallized usin hot ethyl acetate as the solvent heated to 382;C before the solvent was removed usin suction filtration. The crystals were spread on a piece of filter  paper on a watch lass and dried under / lamp for 8 minutes. The yield and the meltin meltin point point of the product was determine determined d usin usin meltin meltin point point apparatus apparatus and weihin balance# respectively. ' small amount of the product was removed usin a capillary tube and dissolved in 3 m! of ethanol to be used for T!C analysis. t is also 8no%n as a Claisen' Schmidt reaction= %hich in"ol"es a reaction bet%een an aldehyde (benzaldehyde and a 8etone 8etone (acetone (acetone catalysed by a base (a!9& (a!9& This reaction is e7othermic e7othermic and th$s releases the heat obser"ed d$e to the t%o dehydration reactions and formation of ne%  bonds in a stable #rod$ct Dibenzalacetone %hich has higher melting and boiling  #oints than the reactants& The e7tensi"e con?$gation of dibenzalacetone ca$ses it to absorb light in the "isible s#ectr$m at @400 nm= res$lting in a yello% colo$r& This is d$e to the delocalisation of electrons in the A clo$d that res$lts in a lo%ering of the  #romotional energy reB$ired for an electron to ?$m# into a higher energy orbital& /ased on the beer eB$ation the energy is lo% eno$gh s$ch that "isible light has eno$ eno$gh gh ener energy gy to allo allo% % the the elect electro rons ns to be #rom #romot oted ed to the the ne7t ne7t orbi orbita tal= l= and and absorbance of #$r#le light near 400nm res$lts in a yello% colo$r& Dibenzalacetone  #reci#itates o$t of the sol$tion beca$se it is not sol$ble in %ater&  1 molar ratio of acetone to benzaldehyde is $sed so that the aldol condensation %ill occ$r on both sides of acetone and yield the most #rod$ct& 9o%e"er= it might still  be #ossible that mono's$bstit$ted acetone (benzylideneacetone might be contaminatin contaminating g in the #rod$ct& /enzylideneac /enzylideneacetone etone has a m$ch lo%er boiling #oint at near *-'4 C com#ared to dibenzaleacetone& >t is of a #aler yello% com#ared to dibenzaleacetone& >n addition= it is also E acti"e d$e to the #resence of the benzene ring& Th$s T