Dibenzalacetone

Aim: To synthesize dibenzalacetone from benzaldehyde and acetone (Aldol condensation) Theory: The purpose of this experiment is to synthesis dibenzalacetone (trans, trans-1,5-diphenyl-

1,4-pe 1,4-penta ntadie dien-3n-3-one) one) throug through h the aldol aldol condens condensati ation on of aceton acetonee ith ith benzald benzaldehyd ehyde! e! The synthesis begins by using strong base to generate the acetone enolate ion! "a "ater ter (not shon) is formed as a byproduct! The e#uilbrium position of this reaction strongly fa$ors the starting acetone, acetone, and the amount amount of acetone acetone enolate enolate formed formed is #uite small% small% hoe$er hoe$er the enolat enolatee is extremely nucleophilic

&eing a $ery strong nucleophile, this enolate attac's the carbonyl of benzaldehyde and forms a &-carb &-carbony onyll al'oxi al'oxide de ion! ion! This This al'oxi al'oxide de ion abstract abstractss a proton proton from ater to form form a beta beta hydroxy hydroxy 'etone! 'etone! odium odium hydrox hydroxide ide abstra abstracts cts another another acidic acidic alpha alpha  to form form a stabil stabilize ized d carbanion! carbanion! The electron electron pair on carbon is used to eliminate eliminate the hyroxide hyroxide ion, forming a alpha beta unsaturated 'etone in an irre$ersible step! This is an example of an *1+& mechanism! ote that in this reaction, the intermediate alcohol is dehydrated under basic conditions, unli'e most alco alcohol hol dehydr dehydrat atio ions ns,, hic hich h are are gener general ally ly *1 mech mechani anism smss under under acid acid condi conditi tions ons!!

The The

*1+& mech mechani anism sm is made made possi possible ble by the the pres presen ence ce of the the carb carbony onyl, l, hic hich h stab stabil iliz izes es the the intermediate carbanion!

ince this nely formed 'etone still posses alpha hydrogens, it too can undergo the same enolate condensation reaction ith a second mole of benzaldehyde to form the final product

Procedure:

&efore you come into lab, ma'e sure you ha$e filled in your table of reagents and products! .ou ill need these $alues (particularly the molecular formula and molecular eight) to determine the identify of your products and to calculate your final yield! Ta'e care to determine the coefficients of the balance chemical reaction hen determining the theoretical yield! /inally, it is important that you 'no exactly hat you are going to be doing so you can or' more efficiently Pocedure: 1! 0ipet into a 52m *rlenmeyer flas' the folloing #uantities 1!43g acetone and 5!5g  benzaldehyde (densities ill be needed to determine the proper $olumes)! ote it is important to maintain a 1 molar ratio of acetone to benzaldehyde! .ou may ha$e to adust your $olumes accordingly! ! dd a magnetic stirring bar to the *rlenmeyer flas' and set the motor for the faster  stirring possible "6T78T splatter!

3! 6n a 122 m bea'er, thoroughly mix 2 m of 9 : sodium hydroxide and 2 m of ;5< ethanol! 4! 0our this mixture into the *rlenmeyer flas' and adust the stirrer motor to maintain maximum stirring! 5! +ontinue to stir for an additional 15 minutes! ote any color changes that may occur! 9! 6solate the product by suction filtration and ash ith +7= ethanol (remember it ta'es a hile to cool the ethanol so plan ahead)! >! +ontinue the suction filtration for an additional 5-12 minutes to allo the product to air  dry! ?! "eigh the crude product and determine its melting point! ;! @ecrystalize your product by dissol$ing it in 15 m of ethyl acetate! 8se lo heat on your hot plate and stir until all of the product dissol$es! tir in 15 m of ;5< ethanol and remo$e from heat! +ontinue to stir constantly until crystals begin to form! 12! +ollect the crystals by suction filtration and allo to air dry for 5-12 minutes! 11! *stimate the purity of your product using 6@ and melting point data

Conclusions  "hy does the acetone enolate preferentially attac' the benzaldehyde rather than another  •

• •

acetone moleculeA o does your 6@ compare to the literature 6@A o pure is your materialA 6s there any e$idence that the purification steps ere effecti$eA

+alculations =ensity of acetone is 2!>; gBml o, 2!>; g ill measure 1 ml o, 1!43 g measures AA ¿

1.43  X  1 0.79

=1.81 ml 2 m l

=ensity of benzaldehyde is 1!24 gBml o, 1!24 g ill measure 1 ml o, 5!5 g measures AAA ¿

5.25  X  1 1.04

=5.04 ml 5 m l