Lab 9- Benzoin Condensation of Benzaldehyde PDF

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Lab 9- Benzoin Condensation of Benzaldehyde...

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5 / 7 / 2 1 La b9:Be n z o i nCo nd e ns a t i o no fBe nz a l d e h y de

I nt r o duc t i o n: Be n z o i nc a nb es y nt h e s i z e dt h r o u g hac on d e ns a t i o nr e a c t i o nb yr e a c t i n gbe nz a l d e h yd ewi t h p o t a s s i u mc y a n i d e( KCN) .Al d e h y d e st h a tl a c ka l p hah y d r o g e n sc a nu n d e r g ot hi sc o nd e n s a t i o n r e a c t i on .I nt h i sr e a c t i o nane wC—Cb o n di sg e ne r a t e dwhe n2mo l so fb e nz a l d e h y d er e a c twi t h KCNt of o r m 1mo lo fb e n z i l .Al t h o u g ht he o r e t i c a l l ya n dp r a c t i c a l l yt h i sr e a c t i o nwo r k sv e r y we l l , p o t a s s i u mc y a n i d es a l t si sav e r yt o x i cr e a g e n t ,a n dc a nbev e r yd a n g e r o u si fn o tu s e dwi t h a b s o l u t ec a u t i o n .An o t he r ,mo r ee n v i r o n me n t a l l yf r i e n d l yo r“ g r e e n e r ”a pp r o a c hwa sd i s c o v e r e d b yu s i n gt h i a mi n eh y d r o c h l o r i d e( Vi t a mi nB1) .Th i sr e a g e n ti sa b l et oe ffe c t i v e l yc a t a l y z et h e b e nz o i nc o n d e n s a t i o nr e a c t i o nb u tl a c kst het o x i ca s p e c t sa n dh a r mf u le n v i r o n me nt a la s p e c t st h a t c o mewi t ht h eKCNr e a c t i o n .Na t ur a l l y ,i two u l db eb e t t e rt ou s et h i a mi n eh yd r o c h l o r i deb e c a u s e i t ’ sas a f e ro p t i o nf o rs t u d e n t sa n dt h ee n v i r o n me nta sawh o l e .

Me t ho dsa ndMa t e r i a l s : Pa r tAo ft h ee x p e r i me n t ,t h eb e n z oi nc o n de n s a t i o nr e a c t i o nwa sp e r f o r me dwi t hKCNa s d e s c r i b e di nt h el a bma n u a l .Pa r tBo ft h ee x p e r i me n ti n c l u de dt h es a mer e a c t i o nb u twa s p e r f o r me dwi t ht het h i a mi n eh y d r o c h l o r i der e a g e n ta sd e s c r i b e di ne xp e r i me n t32 AofPavia, Lampman, Kriz and Engel, A Small Scale Approach to Organic Laboratory Techniques, Fourth Edition, Cengage Learning, 2015, pp 263-264

Re a c t i o na ndMe c ha ni s mf o rPa r tA:

Re a c t i o na ndMe c ha ni s mf o rPa r tB:

Me c hnai s m:

Re s ul t sa ndObs e r v at i o ns : Pa r tA:Be nz o i nc on d e n s a t i o nwi t hKCN:  Ma s so fr e c r y s t a l l i z e dpr o d uc t :1 5 . 4 1 g  Me l t i ngp o i n tofBe nz o i n:1 3 4 . 8 1 3 6 . 2℃  Li t e r a t u r eme l t i n gp o i n to fbe nz o i n :1 3 4 1 3 8 ℃ ( Si g maAl d r i c h ) Pa r tB:Be nz o i nc o nd e ns a t i o nwi t ht h i a mi n ec hl o r i d e  Ma s so fr e c r y s t a l l i z e dpr o d uc t :3 . 4 g  Me l t i ngp o i n tofb e nz o i n :1 3 5 1 3 6. 2℃  Li t e r a t u r eme l t i n gp o i n to fbe nz o i n :1 34 1 3 8 ℃ ( Si g maAl d r i c h ) Re c r y s t a l l i z e dp u r eBe n z o i ns y n t h e s i z e dwa sawh i t es o l i d.

Tr e a t me nto fRe s ul t s :

Pa r tA:Be nz o i nc o nde ns a t i onwi t hKCN:Pe r c e nty i e l dc al c ul a t i o ns : 2 0 mLb e n z a l d e h y d ewa su s e d 2 0 mLC7 H6 O( 1 . 0 44 g / 1 mL)=20 . 8 8go fbe nz a l d e h y d eu s e d 2 0 . 8 8gC7 H6 O(

1mol C 7 H 6 O ) = 0.1967 mols of benzaldehyde. 106.12 g C 7 H 6 O

0.1967 mols of benzaldehyde (

0.0983 mol Benzoin (



1 mol benzoin ) = 0.0983 mol benzoin 2 mol benzaldehyde

212.24 g benzoin )= 20.88g of theoretical benzoin product with KCN 1 mol benzoin

%y i e l d=( 1 5 . 41 g/2 0 . 8 8 g )x1 00=7 3 . 8 %o fBe nz oi npr o duc e dwi t hKCN

Pa r tB:Be nz o i nc o nde ns a t i o nwi t hThi a mi nec hl or i de :Pe r c e nty i e l dc a l c ul a t i ons :

4 . 5mLb e nz a l d e h y d ewa sus e d 4 . 5 mLC7 H6 O( 1 . 0 4 4g / 1 mL)=4 . 7 0go fbe n z a l d e h y d eu s e d 4 . 7 0 gC7 H6 O(

1mol C 7 H 6 O ) = 0.044 mols of benzaldehyde. 106.12 g C 7 H 6 O

0.044 mols of benzaldehyde (

1 mol benzoin ) = 0.0220 mol benzoin 2 mol benzaldehyde

212.24 g benzoin )= 4.70g of theoretical benzoin product with 1 mol benzoin thiamine hydrochloride 0.0220 mol Benzoin (



%y i e l d=( 3 . 4 0g/4 . 7 0 g )x1 0 0=7 2 . 3 %o fBe nz o i npr o duc e dwi t hthiamine hydrochloride

I RSpe c t r ums :

Fi g ur e1 :I Ro fBe nz a l de h ydeRe a c t a nt

Fi g ur e2 :I Ro fBe nz o i nPr o duc t

Di s c us s i o na ndCo nc l us i on:

Bot hr e a c t i o n swe r ep e r f or me da n dh a ds i mi l a ry i e l ds . Fo rt h efir s tr e a c t i onwi t hKCN, 1 5 . 4 1gr a mso fc r u d epr o d u c twa sc o l l e c t e da n da ss e e na bo v et h efir s tr e a c t i onh a dat h e o r e t i c a l y i e l do f2 0. 8 8 g .Th i sp r o vi d e dape r c e n ty i e l dof73 . 8 %. Th i sp e r c e n ty i e l dc o u l dh a v eb e e n l o we r e dd u et oe r r or st h a tc o u l dh a v eo c c u r r e dd u r i ngt hee x p e r i me n tl i k en o tc l e a n i n gg l a s s wa r e p r o p e r l yo rn otp e r f o r mi n gv a c u u mfil t r a t i o np r op e r l yt oc o l l e c td r yp r od u c t .Fu r t h e r mo r e ,i np a r t B, t h i a mi n eh y d r oc h l o r i d ewa su s e d ,a nd3 . 4gr a msofp r od u c twa sc o l l e c t e d . Le s spr o d uc twa s c o l l e c t e db e c a u s el e s ss t a r t i n gma t e r i a lwa sus e d .Th et h e o r e t i c a ly i e l do fb e nz o i np r od u c twa s 4 . 7 0gr a msa ndt hep e r c e nty i e l dob t a i n e dwa s7 2 . 3%. Th ep e r c e n ty i e l dc o u l dh a v eb e e nl o we r e d a l s ob ye r r o r sma dei nt h i se xp e r i me nta ss e e na bo v e . Fo rb o t hr e a c t i o n s ,p e r c e n tyi e l d swe r e f a i r l ys i mi l a ri n d i c a t i n gt h a tb ot hr e a c t i o nsg o tt h ej o bd o n ee ffe c t i v e l y ,b u tt h i a mi ne h y d r o c h l o r i d ei sab e t t e r ,mo r es a f er e a g e ntf ors c i e nt i s t sa ndt hee n vi r o nme n t .Th eme l t i n gp o i n t s o fb o t hp r o d u c t sob t a i n e df r o mb o t hr e a c t i o n swe r ea l s owi t hi nt h el i t e r a t u r ev a l u es i g n i f y i n gt h a t d e s p i t et h eu s eo fdi ffe r e n tr e a g e n t s , t h ep r o d u c e dp r o d u c twa ss t i l lp u r e . Fu r t he r mo r e ,t h eI R’ sofb o t ht h er e a c t a n t sa n dt h epr o d u c t swe r eo b t a i n e da sp i c t u r e d a b o v e .Th eb e nz a l d e h y d er e a c t a n th a ds ha r pp e a k si nt h e1 7 0 0 1 7 50c m-1r e g i o ni n di c a t i n gt h e p r e s e n c eo fac a r bo n y lgr o u pwh i c hi sp r e s e n ti nt hea l d e h y d e . Al s o ,t h e r ewe r et womo d e r a t e l y s h a r pp e a ksa tt h e2 80 0 2 7 0 0c m-1r e g i o nt h a ta r eCHs t r e t c he ss i g n i f yi n gt h ep r e s e nc eo fa n a l de h y d e .Th e r ewa sa l s oa na r oma t i cCHs t r e t c hi nt h e3 0 0 0 3 1 0 0c m-1r e g i o n .Th eb e n z o i n 1 p r o d uc th a das h a r pOHpe a ki nt h e32 0 0 34 0 0c m r e gi o na n das h a r pc a r b o n y lp e a ki nt h e 1 6 8 0 1 7 0 0c m-1r e g i o n .Th i si nd i c a t e dt h a tt h er e a c t i o nwe n tt oc o mp l e t i ona st h eOHgr o u pwa s n o ti nt h eb e n z a l d e h y d er e a c t a n tNMR. As previously mentioned, the thiamine hydrochloride reagent was a greener alternative to the toxic potassium cyanide (KCN). KCN is a very toxic reagent and can be very harmful to humans and the environment. Thiamine hydrochloride however, encompasses the principals of green chemistry to be valued as a more safer option for perform the benzoin condensation with. With the preference of thiamine hydrochloride over cyanide, it prevents excess waste, is nontoxic for humans, is a low risk reagent for chemical accidents, effectively produces benzoin while reducing toxicity, and does not produce toxic gas like HCN. All of these reagents make this reagent green. A drawback with green chemistry is that scientists, when doing these reactions haven’t really taken into account how these dangerous reactions would affect the environment and just in the past few years started to realize. They would much prefer the quicker and dirtier way to get the reagent rather than more environmental friendlier way. Its much more expensive and time consuming to maintain green chemistry techniques that work when the harmful reagents work just as well and get the job done quicker.

Po s tl ab: 1 .

2. There will also be an alcohol peak at 5ppm region and OH attached to CH singlet peak at 6.3ppm. There will be multiplet benzene peaks in the 7-8ppm region. For C-NMR, there will be a new peak at 85ppm for OH attached to C.

Re f e r e nc e s : h t t p s : / / www. s i gma a l d r i c h . c om/ c a t a l o g / p r o d u c t / a l d r i c h / b 8 6 8 1 ? l a n g =e n &r e g i on =US...