OBJECTIVES: This experiment aims to: to: - Produce Produce cyclohex cyclohexene ene thro through ugh the the acid acid catal catalyzed yzed eliminatio elimination n of water water from from cyclohexanol - Successfu Successfully lly use use the the distill distillation ation process process for the dehydratio dehydration n of cyclohexa cyclohexanol nol - Unde Unders rsta tand nd mech mechan anis ism m invol involve ved d in the rea react ctio ion n - Successfu Successfully lly distill distill the cycloh cyclohex exene ene as as soon soon as as it forms forms to prevent prevent the revert reverting ing back to alcohol INTRODUCTION:
The dehydration of an alcohol alcohol is one way to synthesize synthesize alkenes alkenes !n the dehydration of cyclohexanol using phosphoric acid as a catalyst" cyclohexene" cyclohexene" an alkene molecule highly useful in the synthesis of other organic molecules" is produced This dehydration process is considered an elimination reaction" when a base attacks the proton on the ad#acent carbon atom of a carbocation to form an alkene $limination reaction is further promoted by heating which allows the reaction to move to an $% mechanism &n the other hand" the substitution reaction occurs when a nucleophile attacks the carbocation This reaction is used in the substitution of alcohols and is favored with the use of weakly basic nucleophiles 'or this experiment" we will be using the elimination reaction since the reaction medium is acidic PRELAB QUESTIONS: % (hat are are the possible possible side products products in the dehydrat dehydration ion of cyclohexa cyclohexanol) nol) *ow is the formation of these side products minimized+prevented) The dehydration of cyclohexanol cyclohexanol can form form the following side products: products: dicyclohexyl ethers" polymers" mono and dicyclohexyl sulfate These side products can be prevented from forming once the cyclohexene is protonated with an acid The distillation process also removes the alkene from contact with the sulfuric acid" thus acting as the ,rst stage of puri,cation of the alkene *ow is is the yield yield of of the react reaction ion maximize maximized) d) $xplain $xplain The maximization of the the yield is done through the removal removal of the resulting resulting alkene as soon as it is formed This is done to prevent the alkene from reverting back to its alcohol form .istillation aids in this process since alkenes have lower boiling points than alcohols or water water !t is also possible to get a good yield if the substitution reaction is suppressed This is done through the use of strong acids" a high reaction temperature temperature that favors elimination" and distillation of cyclohexene cyclohexene from reaction mixture as it is formed / (hat is the the use of phosphor phosphoric ic acid) 0an 0an it be substitute substituted d with other other acids such such as sulfuric acid or hydrochloric acid) $xplain Phosphoric acid acts as the catalyst in the $% dehydration of cyclohexanol !t protonates the alkene and forms a carbocation which will be attacked by water in order to form an alcohol &ther strong acids may also be used but phosphoric acid" since it is an oxidizing agent" os preferred because it minimizes the loss of the organic compound and the product is not contaminated with volatile decomposition products 1 (hat steps steps are undertak undertaken en to prevent prevent cyclohex cyclohexene ene from from reverting reverting back to cyclohexanol) *ow do these steps prevent reversal from taking place) The removal of the cyclohexene cyclohexene as soon as it forms forms prevents the reverting reverting back to cyclohexanol This removal displaces the reaction to the right 23e 0hatelier4s principle5 2Pahlavan" nd5 6 (hat are are the 7ualitative 7ualitative tests tests to verify verify the presence presence of cyclohex cyclohexene ene and cyclohexanol) (hat constitutes a positive test result) The presence of of cyclohexene cyclohexene can be determined through through a solubility test" an ignition test" and a 8aeyer test The 8aeyer test must form a reddishbrown precipitate to con,rm the presence of cyclohexene 9eanwhile a solubility test" a 3ucas test" and a 0hromic cid test can be done to •
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•
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determine the presence of cyclohexanol The 3ucas test must have the formation of a second phase while the 0hromic cid test must form a bluegreen precipitate
REAGENTS: REAGENTS
PHYSICAL AND CHEMICAL PROPERTIES
Cyclohexanol (IUPAC) [C 6H12O]
Molecular Weight 1!!"161 g#$ol %oiling Point 161"&' oC Melting Point 2"*oC +en,ity !"6 g#c$ * -olu.ility '2/!!! $g#0 (1! oC) in ater Aearance Colorle,, nee3le, or 4i,cou, li5ui3 ith a ca$hor li7e o3or
Pho,horic Aci3 (IUPAC) [H *O'P]
Molecular Weight :"' g#$ol %oiling Point '!: oC Melting Point '2"'oC +en,ity 1"6&! g#c$ * -olu.ility Mi,ci.le in ater Aearance ;hic7/ colorle,,/ o3orle,,/ cry,talline ,oli3
-o3iu$ Hy3roxi3e (IUPAC) [
Molecular Weight *": g#$ol %oiling Point 1*&& oC Melting Point *2*oC +en,ity 2"1* g#c$ * -olu.ility 1! g#1!!$0 (2! oC) in ater Aearance Colorle,, to hite ,oli3/ colorle,, li5ui3/ o3orle,,
-o3iu$ Chlori3e (IUPAC) [Cl
Molecular Weight &"'' g#$ol %oiling Point 1'6 oC Melting Point &!!":oC +en,ity 2"1: g#c$ * -olu.ility *6"! g#1!!g (2 oC) o8 ater Aearance Colorle,, to hite cry,talline ,oli3/ ,alty ta,te
SAFETY PRECAUTIONS
Ha, cau,e3 a34er,e rero3ucti4e an3 8etal e88ect, in ani$al, Potential cancer ha9ar3 -7in an3 eye irritant 8lu,h ith ater 8or at lea,t 1 $in," then get $e3ical a,,i,tance Inge,tion (ha9ar3ou,) 3o not in3uce 4o$iting unle,, in,tructe3 .y $e3ical er,onnel Inhalation (ha9ar3ou,) to 8re,h air/ gi4e oxygen/ ,ee7 $e3ical a,,i,tance Co$.u,ti.le -7in an3 eye irritant 8lu,h ith ater i8 contact -eriou, ,7in contact Wa,h ith 3i,in8ectant ,oa an3 co4er conta$inate3 ,7in ith anti .acterial crea$" -ee7 $e3ical ai3 Inge,tion (ha9ar3ou,) 3o not in3uce 4o$iting unle,, in,tructe3 .y $e3ical er,onnel Inhalation (ha9ar3ou,) re$o4e to 8re,h air/ gi4e oxygen/ ,ee7 $e3ical a,,i,tance -7in an3 eye irritant 8lu,h ith ater i8 contact -eriou, ,7in contact (4ery ha9ar3ou,) Wa,h ith 3i,in8ectant ,oa an3 co4er conta$inate3 ,7in ith anti .acterial crea$" -ee7 $e3ical ai3 Inge,tion 3o not in3uce 4o$iting unle,, in,tructe3 .y $e3ical er,onnel Inhalation re$o4e to 8re,h air/ gi4e oxygen/ ,ee7 $e3ical a,,i,tance Corro,i4e = cau,e, * r3 3egree .urn -7in an3 eye irritant 8lu,h ith ater i8 contact -eriou, ,7in contact Wa,h ith 3i,in8ectant ,oa an3 co4er conta$inate3 ,7in ith anti .acterial crea$" -ee7 $e3ical ai3 Inge,tion 3o not in3uce 4o$iting unle,, in,tructe3 .y $e3ical er,onnel Inhalation re$o4e to 8re,h air/ gi4e oxygen/ ,ee7 $e3ical
+i,o3iu$ -ul8ate (IUPAC) [
Molecular Weight 1'2"!' g#$ol Melting Point &&&oC +en,ity 2"6: g#c$ * Aearance White o3er or orthorho$.ic .iyra$i3al cry,tal,/ o3orle,,/ .itter ,aline ta,te
a,,i,tance -7in an3 eye irritant (ha9ar3ou,) 8lu,h ith ater i8 contact -eriou, ,7in contact Wa,h ith 3i,in8ectant ,oa an3 co4er conta$inate3 ,7in ith anti .acterial crea$" -ee7 $e3ical ai3 Inge,tion 3o not in3uce 4o$iting unle,, in,tructe3 .y $e3ical er,onnel Inhalation re$o4e to 8re,h air/ gi4e oxygen/ ,ee7 $e3ical a,,i,tance
REFERENCES: Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City: Office of Research and Publications, Ateneo de Manila University; 2005. [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information; 2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from: https://pubchem.ncbi.nlm.nih.gov/compound/cyclohexanol [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017 March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9923625 [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information; 2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from: https://pubchem.ncbi.nlm.nih.gov/compound/phosphoric_acid [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017 March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927393 [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information; 2005 March 26 [updated 2017 March 11; cited 2017 March 12]. Available from: https://pubchem.ncbi.nlm.nih.gov/compound/sodium_hydroxide [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017 March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9924998 [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information; 2005 March 25 [updated 2017 March 11 cited 2017 March 12]. Available from: https://pubchem.ncbi.nlm.nih.gov/compound/sodium_chloride [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017 March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927593 [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information; 2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from: https://pubchem.ncbi.nlm.nih.gov/compound/sodium_sulfate [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017 March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927278 Pahlavan. Chem2423 Cyclohexene Synthesis. [Unknown Publication]; [Unknown Publication Date] [cited 2017 March 12]. Available from: http://swc2.hccs.edu/pahlavan/2423L9.pdf -
PROCEDURES:
-et u ,i$le 3i,tillation aaratu," Co4er recei4ing 8la,7 ith alu$inu$ 8oil an3 i$$er,e 8la,7 in iceater .ath"
Place &g o8 cyclohexanol/ 2$0 ho,horic aci3/ an3 .oiling chi, into >%?" Heat $ixture an3 $aintain te$erature .eteen &oC" +i,till until 2*$0 i, le8t in >%?"
Pour 3i,tillate into ,earatory 8unnel an3 a,h it ith $0 o8 * M
Continue a,hing organic layer until a5ueou, layer i, .a,ic then 3i,car3 a5ueou, layer," +ecant organic layer into @rlen$eyer 8la,7 an3 3ry it o4er ,o3iu$ ,ul8ate"
Clean 3i,tillation ,etu ith acetone an3 let 3ry" +i,till organic layer at a te$" not $ore than oC a.o4e .oiling oint o8 cyclohexene"
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Per8or$ 5ualitati4e te,t, an3 ,tore ro3uct in ,cintillating 4ial"
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Cyclohexane i, 4ery 8la$$a.le" ee aay 8ro$ 3irect heat" @4aorate, ea,ily/ 3i88u,e, through cor7 an3 3i,,ol4e, in ru..er" -tore in tightly co4ere3 ,creca 4ial, an3 7ee re8rigerate3"
