Dehydration of Methylcyclohexanol Essay

A common Sophomore radical chemistry laboratory audition that has great potential for further research is the battery-acid catalyzed vapor of simple alcohols. The classic dehyd proportionalityn of 2-methylcyclohexanol essay that was introduced in diary of Chemical Education in 1967 Taber(1967)JCE44,p620. The rather simple procedure of distilling an alcohol with an aqueous acid has spawned several(prenominal) investigations that have resulted in formal daybook articles. At the same meter, the experiment has retained its popularity in the Sophomore Organic Chemistry laboratory curriculum. In one line of inquiry it has been observed that a alloy of 2-methylcyclohexanol diastereomers gives rise to a change of three isomeric alkenes Todd(1994)JCE71,p440 Feigenbaum(1987) JCE64, p273 Cawley (1997) JCE74l, p102.Ex unambiguousing the presence of the three alkene products requires an intense synthesis of information communicated in a typical SOC textbook. The continued popularity o f this experiment is corroborated by the observation that Googling the verbiage dehydration of 2-Methylcyclohexanol on January 13th, 2008 returned no less than 20 hits for online student handouts and/or guides for this SOC laboratory experiment. Moreover, this experiment provides fertile ground for experimentation and innovation that has non yet been fully explored. At Domini back tooth University, the SOC students performed this experiment during the F in all 2007 semester with non only the dehydration of 2-methylcyclohexanol (Aldrich 153087) but in like manner the 4-methyl (Aldrich 153095) and 3-methyl (Aldrich 139734) positional isomers. The reception products were submitted to GC-FID analysis.As predicted from the Journal of Chemical Education articles, three methylcyclohexene products were observed. Their relative abundance metrical by peak height was 80, 16, and 4%. The alkene products represented by these peaks apparently correspond to 1-methycyclehexene, 3-methycycleh exene, and methylenecyclohexane respectively. picThe dehydration of 4-methylcyclohexanol produce two products, that can be lofty by our incumbent GC column, at 90 and 10% with guardianship multiplication that match 3-methycyclehexene and 1-methycyclehexene respectively. My current theory is that the retention times 3 and 4-methycyclohexene could non be distinguished with GC column and temperature program. However, thither is still the issue of how 1-methycyclehexene is produced from 4-methylcyclohexanol. picThe dehydration of 3-methylcyclohexanol yields two products, that can be distinguished by our current GC column, at 80 and 20% with retention times that match 3-methylcyclohexene and 1-methycyclehexene respectively. picSamples of 1-methyl and 3-methyl cyclohexenes purchased from Aldrich chemical confirmed two of compound assignments for the dehydration of 2-methylcyclohexanol. Obviously, it remains to separate the 3 and 4-methylcyclohexene by GC.thither are several advantages of theatre of operationsing the dehydration of methylcyclohexanols in the first semester of Organic Chemistry 1) The experiment involves reactions that are typically studied during first semester E1, E2, and the 1,2-hydride shift. It is a time-tested communications protocol that has been run in hundreds of labs by thousands of students.2) Analysis of the experiment involves the understanding of all three mechanisms mentioned previously and how they whitethorn compete with each unlikewise. In other words, it is a simple experiment that demands a rather involved exposition of results.3) It shows that textbooks rules such as the Zaitzevs rule in this case, are not necessarily rules as such, but rather astute observations of general trends that can vary experimentally depending on the reactant and the reaction conditions.4) Analytically, we are observing/measure the presence of 3 known methylcyclohexene and methylenecyclohexane products that can be separated and find by Gas Chrom atography. I believe that the product mixtures can also be analyzed by NMR.5) The reaction lends itself to an inquiry format that involves the study different reactants and reaction conditions on the ratio of products. In fact, this experiment, in my opinion, is an rarefied candidate for a multi-institution collaborative study that combines and interprets student data.want to postdate point 5 further by first grappling with the current literature concerning the Evelyn Effect. The JCE article by David Todd, The Dehydration of 2-Methylcyclohexanol Revisited The Evelyn Effect observes a energising effect that can be explained by proposing that in a mixture of cis/trans 2-Methylcyclohexanol the cis isomer reacts much faster than the trans isomer to give predominately 1-methylcyclohexene. The formation of 1-methylcyclohexene from cis-2-methylcyclohexanol would involve an E2-like anti- elimination of proton and the protonated alcohol. The dehydration of the trans isomer would go throug h a E1 mechanism that requires the formation of a carbocation forrader elimination of a proton. A follow-up study by Cawley and Linder The Acid Catalyzed Dehydration of an Isomeric 2-Methylcyclohexanol Mixture involves a detailed kinetic study. Students began with a 36.6/63.4 cis/trans mixture of 2-methylcyclohexanol with a cyclohexanol impurity (% impurity was not scoreed).They performed thy typical reaction+ distillment and collected fractions at 4, 8, 16, 24, and 28 minutes. They also collected a 0.1 mL volume of the sample of the reaction mixture at each of these time intervals. These fractions were analyzed by 1H NMR and GC for composition. The cis/trans rate constants for the dehydration of reaction were determined to be 8.4/1.0 much less than 30/1 ratio reported in 1931 by Vavon and Barbier. An intriguing study It would be very evoke to have the raw (student) data on this one. Very lowly is said about the product ratios in the distillate fractions, they just report that they obtained 2.1% methylenecyclohexane and not the 4% previously reported.The dehydration of methylcyclohexanols provides a fecund puzzle to explore. The key is to develop methods to determine the distribution of alkene products in cost of % total alkenes. There are four possible positional isomersI. methylenecyclohexane (Aldrich, Acros, 1192-37-6)II. racemic 3-methyl-1-cyclohexene (Acros, 591-48-0)III. 1-methyl-1-cyclohexene (Aldrich, Acros 591-49-1)IV. racemic 4-methyl-1-cyclohexene (Aldrich, Acros 591-47-9). cardinal of the alkene positional isomers contain an asymmetric carbon.The obvious place to soak up is by studying how the alcohol structure affects the product distribution of alkenes. There are 5 positional isomers of methylcyclohexanol I. cyclohexanemethanol (Aldrich 100-49-2)II. 1-methylcyclohexanol (Aldrich 590-67-0) III. racemic cis&trans 2-methylcyclohexanol (Aldrich 583-59-5) IV. racemic cis&trans 3-methylcyclohexanol (Aldrich 591-23-1) V. cis&trans 4-methylcycl ohexanol (Aldrich 589-91-3).Three of the alcohols are present in cis and trans diastereomer pairs cis 2-methylcyclohexanol (Aldrich 7445-70-1)trans 2-methylcyclohexanol (Aldrich 7445-52-9)cis 3-methylcyclohexanol (5454-79-5)trans 3-methylcyclohexanol (7443-55-2)cis 4-methylcyclohexanol (Aldrich 7731-28-4)trans 4-methylcyclohexanol (Aldrich 7731-28-4).In addition there are 4 entaniomer pairs among the alcohol jump materials. Most of them are commercially available, for a price.picBesides the structure of the alcohol, what other variables may be explored?1) 1 variable for this reaction that could be investigated is the personality of the catalytic acid. Aqueous acids, such as the 85% H3PO4 typically utilize for this experiment, contain some water which is also product of the reaction. I may also add that, the amount of acid is not always in catalytic proportion to the substrate. In my current protocol 0.075 moles of acid is utilize to dehydrate 0.2 moles of alcohol. Non-aqueous a cids may give different results. Acidic resins are an interesting substitute for aqueous acids. For example, John Ludeman and Kurt Field of Bradley University presented a poster at the 2006 ACS Great Lakes Regional Meeting on the use of Dowex 50WX2-100, Amberlite IRC-50S, and Amberlyst 15, for the dehydration of alcohols.2) another(prenominal) variable would be the reaction conditions. In the current paradigm, the alkene is distilled away from the reaction mixture. Presumably, it is being distilled away as it is formed. An ad-hoc observation is that students seem to scotch somewhat different product ratios if they distill is carefully or if they irritable up the heat and distill it quicker. What if the reaction mixture was refluxed to equilibrium before distillation? Would we see more thermodynamic products?3) Reaction conditions could be changed in other ways too. Microwave irradiation is currently being explored as an alternative to heating reactions. Possibly, sonication could also be performed on the alcohol.4) Another boulevard to explore may be different strategies to push the reaction towards the products other than distilling off the alkene. For example, removing water with molecular sieves may be tried.The last initiation of this series volition explore the logistics of dehydration of methylcycohexanols as a collaborative experiments. The most straightforward collaboration would be to perform the dehydration of methylcycohexanols experiment in the same way and compare the relative yield of alkenes as measured by GC from different starting alcohols. Comparisons could be make with past data or concurrently collected data from different institutions. This may be seem fairly straightforward, but there will most likely be discrepancies that could will need to be explored. One aspect to make note of would be the source and composition of the methylcyclohexanols employ a starting materials. Sigma-Aldrich has 1-methylcyclohexanol M38214 2-methylcyclohex anol 66320, 215295, 178829, 24113, & 153087, 3-methylcyclohexanol 139734 4-methylcyclohexanol 66360, 104183, 104191, & 153095 as well as just plain methylcyclohexanol 66370.An experimental variable that is hard to control is rate of heating. Students who crank up the hot plate to get done quickly ( crimson though they were told not to) may get different results than those students who go slowly and maintain an even temperature. Different GC columns and methods may also give results that need to be corroborated.