Hydrogenating ability of Wilkinsons catalyst

Hydrogenating ability of Wilkinsons catalyst Wilkinsons catalyst was prepared from rhodium (III) chloride and refluxed in ethanol with triphenylphosphine, with a measured yield of 72.7%. The efficacy and regioselectivity of Wilkinsons catalyst was then assessed by reaction with carvone in an atmosphere of hydrogen gas at 1 atm, and the product was analysed by 1H-NMR spectroscopy. Introduction Tris-(Triphenylphophine)chloro rhodium(I) was discovered and first profiled by Wilkinson et al in 1965, and noted for its ability to selectively hydrogenate terminal alkenes to alkanes[1]. It was only with the further publishing in 1968 that Wilkinsons catalyst was thoroughly characterised.[2] It was the first homogenous catalyst with the ability to perform this function at a rate similar to that of heterogenous catalysts, without having to resort to high pressures or temperatures in the process. Wilkinsons catalyst is unusual in its ability to easily form a dihydride, despite it being a diphosphine, since these compounds are often either short-lived or difficult to detect.[3] In the above diagram, Wilkinsons catalyst (1) undergoes ligand substitution with a solvent molecule to create the active form of Wilkinsons catalyst (2)[4]. Hydrogen is then attached via oxidative addition (3)4, oxidising Rhodium from +1 to +3 oxidation state and resulting in a change of colour from red to yellow[5]. The prepared catalyst is then injected into the mixture, at which point it complexes with the rhodium centre via the pi bond (4)[6]. The solvent then leaves the complex (5). H migrates to the alkene first due to proximity, with H migrating second[7]. A solvent molecule takes the place of the leaving alkane, converting the catalyst back to its active form (7). The pi bond formed between the alkene and the Rhodium is characterised by back-donation from a d-orbital overlap with the ?* anti-bonding orbital. This back donation, coupled with donation from the ? bond on the alkene results in the ? bond being much weaker and more susceptible to being broken than uncoordinated ethene. 13C-NMR has shown that bonds formed between the a rhodium centre and other alkene complexes bond show significant s-character, typified by downfield shift, or in other words, lack of electron density surrounding them compared to typical alkene spectrum[9]. This lack of electron density makes the carbon atoms very attractive targets for the hydride ligands attached to the Rhodium to migrate to. It is this ability to remove electron density from the alkene ? orbital, while simultaneously back-donating density to the ?* that makes Wilkinsons catalyst so effective. Wilkinsons catalyst cannot hydrogenate areas of conjugation, so theoretically only bond (3) should be hydrogenated in the presence of hydrogen and Wilkinsons catalyst[10]. This experiment will assess the selectivity of the hydrogenating abilities of Wilkinsons catalyst, and its regioselectivity and chemoselectivity in regards to a molecule with several areas capable of hydrogenation. The products in this experiment will be analysed using 1H-NMR data. Experimental Preparation of catalyst Triphenylphosphine (0.52g, 1.98mmol) was dissolved in ethanol (20ml). RhCl3.3H2O (0.08g, 0.3mmol) was dissolved in ethanol (4ml). Both solutions were degassed with nitrogen. The rhodium solution was then added to the PPh3 solution and this was refluxed in a nitrogen atmosphere for 90 minutes. After cooling, the remaining solution and precipitate were removed and filtered via sinter funnel filtration. The yield for the Wilkinson catalyst was determined (0.180g, 0.218mmol, 72.7%). Hydrogenation of carvone Under a pressure of one atmosphere of hydrogen, a flask was injected with the previously prepared catalyst. Carvone (0.5g, 3.33mmol), in a solution of toluene (2ml) was then added to this flask. Consumption of hydrogen, measured using syringes, was recorded at 46cm3, (2.05mmol) representing a 61.6% yield of the hydrogenated carvone product. Results Colour changes Rhodium (III) chloride powder is a black powder. As reflux progressed and the Wilkinsons catalyst was produced, the solution went slowly from black to a brown-red suspension. This is illustrated in figure 4. Hudson et al have also reported an unknown brown precipitate, which appeared to exhibit similar catalytic properties[11]. Wilkinson et al also reported orange precipitate with identical chemical properties[12]. Yields and Errors A total of 0.180g of Wilkinsons catalyst was produced in the experiment, a 72.7% yield, which compares favourably with other studies indicating yields of between 60[13]-88[14]%. 46cm3 of hydrogen gas was absorbed in the process of the experiment, representing a total absorbance of 2.05mmol of hydrogen gas. In passing gas through the solution, it turned yellow, which is consistent with other experimental observations[15] [16]. Considerable agitation of the solution was required so as to allow adequate complexation of the hydrogen gas. Assuming the entirety of this gas hydrogenated the terminal olefin group in carvone; this represents a 61.6% yield of hydrogenation. However, it is entirely likely that a higher yield would have been obtained had the experiment continued for a longer period of time. The yield of hydrogen gas may also be misleading since it is difficult to completely hermetically seal all the apparatus, and it is also difficult to estimate the extent to which gas may have escaped from the reaction vessel. Products obtained from hydrogenation Carvone has several sites available for hydrogenation/reduction. However, RhCl(PPh3)3 will only selectively hydrogenate terminal alkenes, as described by Wilkinson et al. This hypothesis is supported by 1H-NMR data[17] of carvone and the product of hydrogenation. There is no change at peaks 6.69ppm, indicating that this protons environment was not affected by the hydrogenation. The slight downfield shift of the protons of signal between 2.2-2.7ppm to an area between 1.9-2.5ppm indicates that there is less electron density surrounding these protons. These signals were assigned to groups near to the hydrogenated bond, and so this is fairly conclusive evidence that the terminal bond was hydrogenated. The minor signal at 4.72 and 4.75ppm indicate a slight contamination of the sample with carvone. Conclusion The yield obtained by the method followed to synthesize Wilkinsons catalyst afforded values similar to that given in literature. The experiment clearly demonstrated by 1H-NMR data that Wilkinsons catalyst efficiently hydrogenates terminal alkene bonds selectively. A more quantitative study could be performed, wherein systems containing non-conjugated alkene systems were tested for hydrogenation. This would allow more stringent analysis and more precise definition of the hydrogenation abilities of Wilkinsons catalyst. Acknowledgements I would like to thank my demonstrators Mr Adam Bunt and Mr Li-Chen Han for their valuable advice and discussion during the experiment. References J.A.Osborn, G.Wilkinson, J.F.Young, Chem. Comm., 1965, 17 S. Montelatici, A. van der Ent, J. A. Osborn, G. Wilkinson, J. Chem. Soc A, 1968, 1054-1058 Illya D. Dridnev, T. Imamoto, Chem. Commun., 2009, 7447-7464 T. N. Sorrell, Organic Chemistry, University Science Books (2006), pp.503 S. Montelatici, A. van der Ent, J. A. Osborn, G. Wilkinson, J. Chem. Soc A, 1968, 1054-1058 P.S. Kalsi, Stereochemistry Conformation and Mechanism 6th Edition, New Age International (2005), pp.449 M. Carvalho, L. F. Wieserman, D. M. Hercules, App. Spec., Vol. 6, Iss. 3, pp. 290-296 P. Atkins, T. Overton, J Rourke, M. Weller, F. Armstrong, Shriver and Atkins Inorganic Chemistry 8th Edition, Oxford University Press, 2006, pp.536 W. von Phillipsborn, Pure Appl. Chem., Vol. 58, No. 4, pp. 513-528 J. A. Osborn, F. H. Jardine, J. F. Young, G. Wilkinson, J. Chem. Soc. A, 1966, 1711-1732 B. Hudson, P. C. Taylor, D. E. Webster, P. B. Wells, Discuss. Faraday Soc., 1968, 46, 37-47 S. Montelatici, A. van der Ent, J. A. Osborn, G. Wilkinson, J. Chem. Soc A, 1968, 1054-1058 B. Hudson, P. C. Taylor, D. E. Webster, P. B. Wells, Discuss. Faraday Soc., 1968, 46, 37-47 S. Montelatici, A. van der Ent, J. A. Osborn, G. Wilkinson, J. Chem. Soc A, 1968, 1054-1058 S. Montelatici, A. van der Ent, J. A. Osborn, G. Wilkinson, J. Chem. Soc A, 1968, 1054-1058 J. A. Osborn, F. H. Jardine, J. F. Young, G. Wilkinson, J. Chem. Soc. A, 1966, 1711-1732 1H-NMR spectrum data taken from http://dlm.chm.bris.ac.uk/dlm2009-10/file.php/28/resources/Wilkinson_NMR.pdf

effects of television on children :: essays research papers

THE FOLLOWING DESCRIBES THE TERMS ON WHICH EBAY OFFERS YOU ACCESS TO OUR SERVICES. Welcome to eBay Inc.'s User Agreement. This Agreement describes the terms and conditions applicable to your use of our services at http://www.ebay.com and our general principles of our International affiliates. If you have any questions, please refer to our User Agreement Frequently Asked Questions at (http://pages.ebay.com/help/basics/f-agreement.html) or our User Agreement Revision Frequently Asked Questions at (http://pages.ebay.com/help/basics/uarevision1-faq.html). We may amend this Agreement at any time by posting the amended terms on our site. Except as stated below, all amended terms shall automatically be effective 30 days after we initially post them on our site. This Agreement may not be otherwise amended except in writing signed by you and eBay Inc. 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Our changes to the policy are effective after we provide you with at least fourteen (14) days' notice of the changes by posting the changes on the announcements board. However, we may choose to temporarily change our Fees and Credits Policy and the fees for our services for promotional events (for example, free listing days) and such changes are effective when we post the temporary promotional event on the announcements board. When you list an item you have an opportunity to review and accept the fees that you will be charged for the use of our listing services. We may in our sole discretion change some or all of our services at any time. In the event we introduce a new service, the fees for that service are effect ive at the launch of the service. Unless otherwise stated, all fees are quoted in U. effects of television on children :: essays research papers THE FOLLOWING DESCRIBES THE TERMS ON WHICH EBAY OFFERS YOU ACCESS TO OUR SERVICES. Welcome to eBay Inc.'s User Agreement. This Agreement describes the terms and conditions applicable to your use of our services at http://www.ebay.com and our general principles of our International affiliates. If you have any questions, please refer to our User Agreement Frequently Asked Questions at (http://pages.ebay.com/help/basics/f-agreement.html) or our User Agreement Revision Frequently Asked Questions at (http://pages.ebay.com/help/basics/uarevision1-faq.html). We may amend this Agreement at any time by posting the amended terms on our site. Except as stated below, all amended terms shall automatically be effective 30 days after we initially post them on our site. This Agreement may not be otherwise amended except in writing signed by you and eBay Inc. This agreement is effective on March 21st, 2001 for new registering users, and is otherwise effective on May 15th, 2001 for all users registered prior to March 21st, 2001. 1. Membership Eligibility. Our services are available only to individuals who can form legally binding contracts under applicable law. Without limiting the foregoing, our services are not available to minors or to temporarily or indefinitely suspended eBay members. If you do not qualify, please do not use our services. Further, your eBay account (including feedback) and User Id may not be transferred or sold to another party. 2. Fees and Services. Joining and bidding on items at eBay is free. Our Fees and Credits Policy is available (at http://pages.ebay.com/help/sellerguide/selling-fees.html) and is incorporated by reference. We may change our Fees and Credits Policy and the fees for our services from time to time. Our changes to the policy are effective after we provide you with at least fourteen (14) days' notice of the changes by posting the changes on the announcements board. However, we may choose to temporarily change our Fees and Credits Policy and the fees for our services for promotional events (for example, free listing days) and such changes are effective when we post the temporary promotional event on the announcements board. When you list an item you have an opportunity to review and accept the fees that you will be charged for the use of our listing services. We may in our sole discretion change some or all of our services at any time. In the event we introduce a new service, the fees for that service are effect ive at the launch of the service. Unless otherwise stated, all fees are quoted in U.

Judaism and Passover

* This essay will describe Passover a Jewish Holy Days. This essay will discuss the time of the year of the holy day(s), the historic origin of the holy day(s), and the religious practices associated with the day(s). This essay will also identify the theological or cultural differences that may lead to differences in the observance of the holy day by the various branches of Judaism. * Passover is a Jewish holidays, best known maybe because Christian history, the Last Supper was said to be a Passover meal. The last and greatest of the plagues is the death of the first-born sons of the Egyptians.The Israelite’s son weren’t killed because they have followed Yahweh’s warning and have marked the doors of their homes with the blood of a substitute – a sacrificial lamb (Exod. 12:13). Because God has â€Å"passed over† Egypt, the event is thereafter called the Passover or Pesach, and its yearly memorial has become one of the major Jewish festivals. Passover begins on the 15th day of Nissan (Nissan is 30 days between March-April). Passover is the first of the three major holidays (Passover, Shavu’ot and Sukkot) with both historical and agricultural significance.Historically Passover observes the Exodus from Egypt after many years as slave to the Egyptians, as told in Exodus. Agricultural receives little attention, it is the beginning of the harvest season in Israel. The weeklong holiday of Passover starts on the first lunar month and may have originally begun as a renewal springtime nature day. It recalls the Hebrew’s escape from Egypt slavery. Placing lamb blood from the Passover meal, as told in Book of Exodus, over the doors of the Hebrews, keeps the angel of death from killing their first born sons and the power of God â€Å"passed over† Egypt.The Passover Meal is a memorial meal, the Seder or order, at which Jews eat several symbolic foods (bread, a meal, salad of nuts and fruits). The bread, a thin flat bread called matzah, does not have yeast. Matzah shows how there was no time for bread to rise in the Hebrews’ rush to leave Egypt. This is also refer to as chametz (leaven; sounds like â€Å"hum it's† with that Scottish â€Å"ch†), it symbolizes a way of removing the â€Å"puffiness, arrogance, pride† from their souls. Chametz includes anything made from the five major grains (wheat, rye, barley, oats, and spelt) that have not been completely cooked within 18 minutes after coming into contact with water† (Judaism 101). A shank bone of lamb or other animal is in the meal, symbolizing the sacrificial lamb. A salad of nuts and fruits, or haroseth, symbolizes the mortar used by the Hebrews in their forced labor. To remember the suffering of the Hebrews during their oppression, diners dip parsley in saltwater and eat bitter herbs. During the meal the story of Moses, and the Israelites is retold.A place and cup of wine is set up at the table for the prophet E lijah, â€Å"actions representing the hope that he will return to earth to announce the coming of the Messiah. A delicious meal follows the ritual part of the supper. Today many Jews invite non-Jews to share in their Seder and celebration of Jewish customs† (Molloy (2010)). The text of the Passover seder is written in a book called the Haggadah. â€Å"Orthodox Jews of Ashkenazic background also avoid rice, corn, peanuts, and legumes (beans) as if they were chametz.All of these items are commonly used to make bread, thus use of them was prohibited to avoid any confusion. Such additional items are referred to as kitniyot† (Judaism 101). * In conclusion this essay described Passover. The essay discussed the time of the year of the holy day(s), the historic origin of the holy day(s), and the religious practices associated with the day(s). This essay also identified the theological or cultural differences that may lead to differences in the observance of the holy day by the various branches of Judaism.

The Long Journey Undertaken By Indigenous Australians

The long journey undertaken by indigenous Australians in their search for equality, respect and legal ownership of what is rightfully theirs, has been a long, bloody battle spanning the last 200 years and unfortunately remains largely unresolved. The Close the Gap Campaign is one example of positive attempts to strengthen the indigenous / white relationship as it offers numerous support systems for the indigenous, from the government. Another example of such positive steps is seen in 2008, when the then Prime Minister, Kevin Rudd made an emotional speech to apologise to the Aborigines and Torres Strait Islanders for the terrible suffering and heart wrenching battle they have experienced before, during and long after the Stolen Generation†¦show more content†¦The British killed thousands of Indigenous people including whole families; they stole away the land that the Indigenous Australians had been spiritually connected to their whole lives. Another disaster for the aborigin als was that the Europeans brought diseases and famine to the country which killed a major percentage of the population. The British were taking what the Indigenous rightfully owned and started to destroy and change it drastically. The Indigenous had to abide by the European rules and had to change their culture and beliefs to fit in. The Apology speech by former Prime Minister, Kevin Rudd, was presented in front of Indigenous Australians that were and were not affected by the Stolen Generation and also non-indigenous Australians. Both indigenous and white Australians have their opinion on The Apology regarding what it means for them, what it has resolved or if it has added fuel to the fire. Mr Gary Foley, a long time Indigenous activist outlined his views when stating; â€Å"I think it should be taught in Political Science classes as an example of the duplicity and deceit of politicians. And it should be taught in psychology classes in terms of how a nation appeases itself of its guilt. And it should be taught in drama school as a classic example of Australian political comedy. And it should be taught in driving school as a magnificent example of defensive driving and evasive tactics and