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Preparation Preparation and Purifcation o an Alkyl Halide Joshua L. Chuaa* a
Department of Chemical Engineering, University of the Philippines Diliman, Quezon City, Philippines
AB!"AC! #$utyl alcohol %as reacted %ith a hydrogen halide &hydrochloric acid' to produce tert #$utyl #$utyl chloride. !he reaction %as carried out Tert #$utyl (ia nucleophilic su$stition &specifcally) &specifcally) an 1 +echani +echanis+' s+'.. Cold Cold concentr concentrate ated d HCl %as added in e,ces e,cess s to tert #$utyl #$utyl alcohol. alcohol. Ater%ards) solid aHC- and anhydrous CaCl/ %ere added to puriy the co+pound and to +aintain the product as an alkyl halide. 0inally) the crude tert #$utyl #$utyl chloride %as distilled to o$tain pure tert #$utyl #$utyl chloride. /. g o tert #$utyl #$utyl chloride %as o$tained o$tained ater distillation. 2ith a theoretical yield o .31/ g) the 4 yield %as /.354. 2hile crude tert #$utyl #$utyl chloride %as successully synthesi6ed ro+ tert #$utyl #$utyl alcohol) the e,peri+enters ailed to o$tain a signifcant a+ount o pure product) %ith a percent yield o 784.
*Corresponding author. 9o$ile: 8155;85/<8 8155;85/<8 =#+ail address: >oshua.chua./?g+ail.co+
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1. Introduction
Alcohols are an organic co+pound %herein a hydro,yl group -H' is $onded to a sp hy$ridi6ed car$on. 2hen reacted %ith hydrogen halides &such as HCl') alcohols can undergo a nucleophilic su$stitution reaction to or+ an alkyl halide. @n this e,peri+ent) tert #$utyl alcohol is reacted %ith concentrated hydrochloric acid to or+ tert #$utyl chloride. !his reaction occurs (ia an 1 +echanis+. 1 reactions are nucleophilic reactions %here the rate# deter+ining step is uni+olecular &9c9urry) /81'. Alkyl halides are si+ply alkanes containing one or +ore halogens. 2hile nor+al alkanes are non#polar) alkyl halides are polar co+pounds. !his is due to the electronegati(e nature o halogens. @n the C# $ond) the car$on e,hi$its a partial positi(e charge %hile the halogen e,hi$its a partial negati(e charge. Alkyl halides can $e classifed into types: pri+ary) secondary) and tertiary. Pri+ary alkyl halides are co+pounds %herein the car$on that is $onded to the halogen is $onded to only 1 other car$on. Like%ise) the car$on %ith the halogen attached in secondary alkyl halides are $onded to / other car$ons %hile in tertiary alkyl halides the car$on is attached to other car$ons. An e,a+ple o a tertiary alkyl halide is tert #$utyl chloride) the fnal product o this e,peri+ent. As ar as physical properties go) alkyl halides ha(e higher $oiling points co+pared to alkanes. !his is due to the increase in si6e o the +olecule $y replacing a hydrogen %ith a halogen. Alkyl halides are also solu$le in organic sol(ents $ut are only slightly solu$le in %ater. @n the e,peri+ent) tert #$utyl alcohol is reacted %ith concentrated hydrochloric acid to synthesi6e tert #$utyl chloride. Ater%ards) tert #$utyl chloride is purifed (ia distillation.
A si+ple distillation set#up %as prepared) +aking sure that the %ater Do%ed into the $otto+ o the condenserFs cooling >acket and out ro+ the top. A ther+o+eter $ul$ %as placed >ust $elo% the side ar+ o the distillation head. A round $otto+ Dask %as chosen to place the sa+ple in. A %ater $ath %as used to regulate the te+perature. /# pieces o $oiling chips %ere added to the Dask. !he %ater supply %as turned on and the sa+ple in the Dask %as slo%ly heated to a gentle $oil. !he $oiling point %as recorded. !he heat %as ad>usted so that the distillation occurred at a rate o / drops o distillate per second. !he frst e% +illiliters o distillate %ere discarded %hile the raction that distilled at the desired te+perature %as collected. !his %as recorded as the $oiling point o the (olatile co+ponent. !he distillation set#up %as +aintained until right $eore the sa+ple %as dried up. !he heat source %as re+o(ed %hen the sa+ple started to $oil. 0inally) the set#up %as allo%ed to cool $eore dis+antle+ent. 3. Results and Discussion
@n the e,peri+ent) a tertiary alcohol & tert #$utyl alcohol' %as reacted %ith a hydrogen halide &concentrated hydrogen chloride' to synthesi6e an alkyl halide &tert #$utyl chloride'. !his reaction %as done (ia an 1 +echanis+. !he +echanis+ is sho%n in the fgure $elo%:
2. Materials and Methods 2.1. eneration of Cru!e tert"#utyl Chlori!e
18 +L o tert #$utyl alcohol and /8 +L o cold concentrated HCl %ere placed in a dry 8 +L separatory unnel. !he +i,ture %as s%irled gently %hile occasionally relie(ing the internal pressure $y opening the stopcock. !he +i,ture %as allo%ed to stand undistur$ed or /8 +inutes. !he separation o layers %as acilitated $y adding # +L o 5 9 aCl solution. !he aueous layer %as then discarded. 1#/ drops o %ater %as added to the separated layers to deter+ine the identity o the organic layer. !he collected fltrate %as dried %ith a s+all a+ount o anhydrous CaCl/. +all a+ounts %ere added until it clu+ped together. !he crude tert #$utyl chloride %as decanted into a dry / +L round $otto+ Dask. A e% $oiling chips %ere added and the Dask %as distilled. !he raction that $oiled at ;#/EC %as collected in a pre#%eighed (ial and cooled in an ice $ath. !he percent yield %as deter+ined and the solu$ility o the purifed product %as tested %ith %ater. !he %astes %ere then disposed into the appropriate %aste containers. 2.2. Preparing a $imple Distillation %pparatus
&ource: http:GGacade+ic.keystone.eduGJ0alconeGtBuClPrep(/flesGi+age88;.gi'
Fig. 1. 1 reaction +echanis+ or tert #$utyl alcohol and hydrochloric acid
Aside ro+ tert #$utyl chloride) +ethylpropene +ay also $e produced as a side product. !his +ay happen i the reaction is done at ele(ated te+peratures. !o a(oid the or+ation o +ethylpropene) the concentrated HCl is cooled do%n $eore $eing added to the tert #$utyl alcohol. Another +ethod o li+iting the a+ount o +ethylpropene is to occasionally open the stopcock o the separatory unnel %hen s%irling. !his is done in order to release the gaseous +ethylpropene. Cold concentrated HCl %as added in e,cess or t%o reasons. 0irst) as stated a$o(e) the cooled do%n HCl pre(ents the production o other un%anted side products. econd) adding the HCl in e,cess ensures that the reaction proceeds in the or%ard direction &i.e.) to%ards the or+ation o tert #$utyl chloride'. Ater collecting the organic layer) solid aHC- %as added to it. !his %as done in order to react %ith and
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neutrali6e the e,cess HCl. Aueous aHC- %asnFt used or it %ould re(erse the reaction and produce tert #$utyl alcohol. Ater the addition o aHC-) anhydrous CaCl/ %as added to the crude product. Adding CaCl / pre(ents the hydrolysis o the tert #$utyl chloride. -ther%ise) the product +ay re(ert $ack to the original alcohol. !he CaCl/ also a$sor$s any e,cess %ater. !o isolate and protect the target co+pound ro+ possi$le i+purities) as %ell as to puriy the product) the sa+ple %as distilled using a si+ple distillation set#up. Boiling chips %ere used during distillation to pro(ide nucleation sites so that the liuid $oiled s+oothly. A continuous Do% o %ater %as also part o the set#up so that the sa+ple condenses ater heating and not e(aporate. Ater distillation) the +ass and percent yield o tert # $utyl chloride %as o$tained. Belo% is a ta$le o the +asses o the $eginning and end products) along %ith the theoretical and 4 yield. Table 1 9asses o "eactants I Products and ield Mass of tert -butyl alcohol,<.33 g g Mass of tert -butyl/. g chloride, g !heoretical yield .31/ g 4 yield /.35 4
Table 2 Physical Properties o tert #Butyl Alcohol and tert #Butyl Chloride Proerties tert -!utyl "lcohol tert -!utyl #hloride Color colorless colorless olu$ility in %ater solu$le insolu$le Boiling point 3/.;1EC 1EC
@t %as o$ser(ed that the tert #$utyl chloride is less solu$le in %ater than the original alcohol and also has a lo%er $oiling te+perature. $. #onclusion and Reco%%endations
Crude tert #$utyl chloride %as successully synthesi6ed ro+ tert #$utyl alcohol and concentrated hydrochloric acid. Ho%e(er) in ter+s o the a+ount o tert # $utyl chloride produced) the e,peri+ent %as a ailure $ecause o the lo% percent yield. !he +ethodology can $e i+pro(ed $y storing the crude tert # $utyl chloride %hen not in use to pre(ent e(aporation o the product. References Pa(ia) K. 9c9urry) J. &rganic Chemistry )
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!he relati(ely lo% yield can $e attri$uted to the (olatility o alkyl halides) such as tert #$utyl chloride &Pa(ia) /88'. Lea(ing the product alone and e,posed to open air +ay ha(e e(aporated so+e o the alkyl halide. Peror+ing the e,peri+ent aster and +ini+i6ing the e,posure ti+e o the product to open air +ay $e done to increase the percent yield. Belo% is a ta$le o the o$ser(ed and +easured physical properties o tert #$utyl alcohol and tert #$utyl chloride.
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"apra !echnology. "igid PMC 0oa+s: A e% !%ist to an -ld !echnology. Cellular Polymers ''' . 1) 1;. NC Ka(is Che+2iki. http:GGche+%iki.ucda(is.eduG &accessed 9arch /) /815'.
"endices
&ee attached data sheet'