'Dehydration of Methylcyclohexanol Essay\r'

'A common soph native Chemistry laboratory taste that has great potential for further enquiry is the tart catalyzed vaporisation of simple alcohols. The unstained vaporisation of 2-methylcyclohexanol essay that was introduced in ledger of Chemical schooling in 1967 Taber(1967)JCE:44,p620. The quite simple procedure of di shut uping an alcohol with an aqueous acid has spawned several investigations that have resulted in formal journal articles. At the same clipping, the experiment has retained its popularity in the sophomore(prenominal) Organic Chemistry laboratory curriculum. In one line of inquiry it has been ascertained that a intermixture of 2-methylcyclohexanol diastereomers cash in ones chipss rise to a mixture of three isomeric olefines Todd(1994)JCE:71,p440; Feigenbaum(1987) JCE:64, p273; Cawley (1997) JCE:74l, p102.\r\nExplaining the heading of the three alkene intersection points requires an intense subtraction of information communicated in a classifia ble SOC textbook. The continued popularity of this experiment is corroborated by the an nonation that Googling the phrase â€Å"Dehyd symmetryn of 2-Methylcyclohexanol” on January 13th, 2008 returned no less than 20 hits for online pupil handouts and/or guides for this SOC laboratory experiment. Moreover, this experiment provides fertile consideration for experimentation and innovation that has not b bely been fully lookd. At Domini squirt University, the SOC students performed this experiment during the F alto rewardher 2007 semester with not only the dehydration of 2-methylcyclohexanol (Aldrich 153087) only when in like manner the 4-methyl (Aldrich 153095) and 3-methyl (Aldrich 139734) positional isomers. The response products were submitted to GC-FID analysis.\r\nAs predicted from the Journal of Chemical Education articles, three methylcyclohexene products were observed. Their coition abundance heedful by peak height was 80, 16, and 4%. The alkene products repre sented by these peaks throwmingly correspond to 1-methycyclehexene, 3-methycyclehexene, and methylenecyclohexane respectively. [pic]\r\nThe dehydration of 4-methylcyclohexanol produce cardinal products, that post be baronial by our latest GC column, at 90 and 10% with retention times that equip 3-methycyclehexene and 1-methycyclehexene respectively. My current theory is that the retention times 3 and 4-methycyclohexene could not be distinguished with GC column and temperature program. However, there is still the issue of how 1-methycyclehexene is produced from 4-methylcyclohexanol. [pic]\r\nThe dehydration of 3-methylcyclohexanol yields two products, that goat be distinguished by our current GC column, at 80 and 20% with retention times that match 3-methylcyclohexene and 1-methycyclehexene respectively. [pic]\r\nS vitamin Aereles of 1-methyl and 3-methyl cyclohexenes purchased from Aldrich chemic confirmed two of compound assignments for the dehydration of 2-methylcyclohe xanol. Obviously, it remains to separate the 3 and 4-methylcyclohexene by GC.\r\nThere argon several advantages of perusing the dehydration of methylcyclohexanols in the first semester of Organic Chemistry: 1) The experiment feigns receptions that ar typically studied during first semester: E1, E2, and the 1,2-hydride shift. It is a dependable protocol that has been run in hundreds of labs by thousands of students.\r\n2) Analysis of the experiment involves the understanding of all three mechanisms mentioned previously and how they may deal with each other. In other words, it is a simple experiment that demands a sooner involved interpretation of results.\r\n3) It shows that textbooks â€Å"rules” such(prenominal) as the Zaitzev’s 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 chemical reaction conditions.\r\n4) Analytically, we are observing/meas uring the presence of 3 known methylcyclohexene and methylenecyclohexane products that can be separated and detected by fellate Chromatography. I believe that the product mixtures can in addition be analyzed by NMR.\r\n5) The reaction lends itself to an inquiry format that involves the matter diverse reactants and reaction conditions on the ratio of products. In fact, this experiment, in my opinion, is an ideal panorama for a multi-institution collaborative study that combines and interprets student data.\r\nwant to pursue point #5 further by first scramble by with the current literature concerning the â€Å"Evelyn Effect.” The JCE article by David Todd, â€Å"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(prenominal) faster than the trans isomer to communicate predominately 1-methylcyclohexene . The formation of 1-methylcyclohexene from cis-2-methylcyclohexanol would involve an â€Å"E2-like” anti-elimination of proton and the protonated alcohol. The dehydration of the trans isomer would go through a E1 mechanism that requires the formation of a carbocation onwards elimination of a proton. A implement study by Cawley and Linder: â€Å"The Acid Catalyzed Dehydration of an Isomeric 2-Methylcyclohexanol Mixture” involves a comminuted kinetic study. Students began with a 36.6/63.4 cis/trans mixture of 2-methylcyclohexanol with a cyclohexanol impurity (% impurity was not reported).\r\nThey performed thy typical reaction+ draw outation 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 art object. The cis/trans rate constants for the dehydration of reaction were headstrong 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 kindle to have the earthy (student) data on this one. Very elfin 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.\r\nThe dehydration of methylcyclohexanols provides a fecund problem to explore. The key is to interrupt methods to determine the distribution of alkene products in terms of % total alkenes. There are four possible positional isomers:\r\nI. methylenecyclohexane (Aldrich, Acros, 1192-37-6);\r\nII. racemic 3-methyl-1-cyclohexene (Acros, 591-48-0);\r\nIII. 1-methyl-1-cyclohexene (Aldrich, Acros 591-49-1)\r\nIV. racemic 4-methyl-1-cyclohexene (Aldrich, Acros 591-47-9). twain of the alkene positional isomers contain an noninterchangeable carbon.\r\nThe obvious place to start 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);\r\nII. 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-methylcyclohexanol (Aldrich 589-91-3).\r\nThree of the alcohols are present in cis and trans diastereomer pairs: cis 2-methylcyclohexanol (Aldrich 7445-70-1)\r\ntrans 2-methylcyclohexanol (Aldrich 7445-52-9)\r\ncis 3-methylcyclohexanol (5454-79-5)\r\ntrans 3-methylcyclohexanol (7443-55-2)\r\ncis 4-methylcyclohexanol (Aldrich 7731-28-4)\r\ntrans 4-methylcyclohexanol (Aldrich 7731-28-4).\r\nIn addition there are 4 entaniomer pairs among the alcohol starting materials. more or less of them are commercially available, for a price.\r\n[pic]\r\n at any rate the structure of the alcohol, what other multivariates may be explored?\r\n1) One variable for this reaction that could be investigated is the nat ure of the catalytic acid. Aqueous acids, such as the 85% H3PO4 typically utilize for this experiment, contain some pissing which is also product of the reaction. I may also add that, the amount of acid is not always in catalytic likeness to the substrate. In my current protocol 0.075 moles of acid is officed to dehydrate 0.2 moles of alcohol. Non-aqueous acids may give different results. Acidic resins are an interesting substitute for aqueous acids. For example, John Ludeman and Kurt line of business of Bradley University presented a poster at the 2006 ACS swell Lakes Regional Meeting on the use of Dowex 50WX2-100, Amberlite IRC-50S, and Amberlyst 15, for the dehydration of alcohols.\r\n2) Another variable would be the reaction conditions. In the current paradigm, the alkene is distilled outside from the reaction mixture. Presumably, it is being distilled away as it is formed. An ad-hoc observation is that students seem to get somewhat different product ratios if they distill is carefully or if they â€Å" starter up the heat” and distill it quicker. What if the reaction mixture was refluxed to equilibrium before distillation? Would we see more thermodynamic products?\r\n3) Reaction conditions could be changed in other ways too. vaporize irradiation is currently being explored as an alternative to heating reactions. Possibly, sonication could also be performed on the alcohol.\r\n4) Another avenue to explore may be different strategies to repulse the reaction towards the products other than distilling off the alkene. For example, removing water with molecular sieves may be tried.\r\nThe blend in installment of this series will explore the logistics of â€Å"dehydration of methylcycohexanols” as a collaborative experiments. The nigh straightforward collaboration would be to perform the â€Å"dehydration of methylcycohexanols” experiment in the same way and compare the relative yield of alkenes as measured by GC from different star ting alcohols. Comparisons could be made with past data or concurrently collected data from different institutions. This may be seem clean straightforward, but there will most likely be discrepancies that could will involve to be explored. One aspect to coiffe note of would be the source and composition of the methylcyclohexanols used a starting materials. Sigma-Aldrich has\r\n• 1-methylcyclohexanol #M38214;\r\n• 2-methylcyclohexanol #66320, #215295, #178829, #24113, & #153087,\r\n• 3-methylcyclohexanol #139734;\r\n• 4-methylcyclohexanol #66360, #104183, #104191, & #153095;\r\n• as well as just plain methylcyclohexanol #66370.\r\nAn experimental variable that is hard to control is rate of heating. Students who crank up the hot plate to get done quickly (even though they were told not to) may get different results than those students who go slowly and maintain an even temperature. several(predicate) GC columns and methods may also give result s that need to be corroborated.\r\n'