Preparation of Cyclohexanol Intro PDF

Preview

Summary

chemistry lab Multistep Synthesis of Acetylsalicylic Acid Procedure Your research needs cyclohexanol to progress, and you cannot wait. Therefore you need to make the required 20 grams. You have both cyclohexene and cyclohexanone available. You must choose which route that you are going to use to mak...

Description

CYCLOHEXANOL

EXPERIMENT #4

PREPARATION OF CYCLOHEXANOL LEARNING OBJECTIVES: ❖ To be able to develop a protocol for a reaction without step by step instructions ❖ Introduction to proposal creation. Increase written ability ❖ Produce, purify, and then test the purity of a marketable product Introduction It has often been said that necessity is the mother of invention. For this experiment you need 20 grams of cyclohexanol. When you go to the storeroom, the bottle is empty and when you try to order it, you find that it is on backorder.

Your research needs cyclohexanol to progress, and you cannot wait. Therefore you need to make the required 20 grams. You have both cyclohexene and cyclohexanone available. You must choose which route that you are going to use to make the cyclohexanol. You will need to create a proposal showing the procedure that you will follow. The proposal must show justifications for the choices that you made with respect to the procedure for making the cyclohexanol. Please determine the cost of making the cyclohexanol. Be sure to include the cost of all reagents, and factor in your time. You can assume that we have the basic organic glassware, so these do not need to be part of the cost analysis. Be sure to include all pertinent physical data about your reactants and product. You will be working with your partner in the lab, but you need to produce your own proposa l. Please discuss with your partner how you intend to make the cyclohexanol but please ensure that you do not commit academic misconduct by copying from each other.

CYCLOHEXANOL

EXPERIMENT #4

CYCLOHEXENE OPTION: HYDRATION OF AN ALKENE This is an acid catalysed addition. The acid that would be available would be sulphuric acid. Please be mindful that this is an exothermic reaction and that cyclohexene is volatile. Adding water would be a good source of hydroxyl groups. Overall Reaction H2SO4 H2O

Cyclohexene

Cyclohexanol

Initially, cyclohexene is insoluble in the water-acid solution and appears as a two-phase mixture. Cyclohexene will react with water and also with sulfuric acid to form two products: protonated cyclohexanol and cyclohexyl hydrogen sulfate. Both of these products are soluble in the water -acid solution, therefore, when the original two-phase mixture becomes homogeneous, the reaction is complete. In practice, the degree of homogeneity is difficult to distinguish because of darkening of the reaction mixture from cationic polymerization of cyclohexene. Cyclohexanol is isolated from the reaction mixture by dilution with water followed by steam distillation. When the water is added, a two-phase system results: an upper layer of cyclohexanol and a lower layer of aqueous acid. When this mixture is heated, the cyclohexyl hydrogen sulfate by-product is converted to protonated cyclohexanol that is in equilibrium with cyclohexanol. Steam distillation separates the organic compounds from the sulfuric acid solution. The distillate consists primarily of cyclohexanol and water plus a small amount of cyclohexene. Because cyclohexanol and water form an azeotrope that boils at 98°C, the bulk of the material distills at this temperature. An azeotrope is a mixture of two or three compounds which, when distilled, exhibit a fixed boiling point, like that of a pure compound. Salting out is a technique commonly used in extractions; its main purpose is to improve the yield of the product. Salting out is done by adding enough salt to the aqueous phase to make it a saturated solution. Salt helps to remove the organic compound from the aqueous phase by reducing the solubility of the organic compound in water, forcing a transfer of the organic compound out of the aqueous phase and into the organic phase. This step is followed by the separation of the organic phase from the aqueous phase. As a further precaution against mechanical loss (droplets clinging to the separatory funnel, etc.), diethyl ether is used to extract the cyclohexanol from the salt-water mixture. After separation, the organic layer is dried prior to distillation. Anhydrous magnesium sulfate is a suitable drying agent; however, anhydrous potassium carbonate is the agent of choice because it will neutralize any trace of acid that may have been carried through the work-up procedure. In the final distillation, a trace of acid would cause dehydration of the cyclohexanol.

CYCLOHEXANOL

Tips -

EXPERIMENT #4

14 mL of sulphuric acid would be a suitable volume for catalysis. Ice will be available to keep your reaction flask cool You should vigorously shake the reaction mixture for at least 30 minutes to ensure the reaction proceeds towards the products. Vent periodically to prevent pressure build up. Please ensure that boiling chips and vacuum grease are used when performing a distillation, and using ground glass The amount of salt required to make a saturated solution can be calculated in advance. It would be good to take note of any boiling points that were observed in both of the distillations Parafilm will be available to store your sample after salting it out. This would be a good place to break after the first lab session. Diethyl ether will be available on the second lab session for extractions. Potassium carbonate will also be available on the second lab session to dry your sample and neutralize any excess acid. After your final distillation, be sure to measure the quantity that you actually made (compare this to the amount theoretically possible). Do not boil to dryness. Also be sure to test the purity of your sample (indicate in your proposal how you intend to do this).

CYCLOHEXANOL

EXPERIMENT #4

CYCLOHEXANONE OPTION: REDUCTION OF A KETONE Reducing cyclohexanone to cyclohexanol is a second option that you have. The reduction reaction can be accomplished several ways but there are many factors to take into consideration in choosing which is best suited for your purpose. Metal hydrides of the Group III elements were first discovered in 1943, and were found to be very useful reducing agents. Lithium aluminum hydride, LiAlH4, reduces many compounds containing carbonyl groups, such as aldehydes, ketones, carboxylic acids, esters and amides. Sodium borohydride, NaBH 4, is less reactive and therefore can only reduce aldehydes and ketones to primary and secondary alcohols. Sodium borohydride is mainly used in organic synthesis, while lithium aluminum hydride is used in organic synthesis and other applications. Before these metal hydrides were known, carbonyl groups were reduced to alcohols by treatment with hydrogen (H 2) and sodium metal. All the metal hydrides work by providing a hydride (H:-) that will act as a nucleophile to attack the electrophilic carbonyl carbon; however, no free hydride ions are generated in solution. Kinetic studies indicate that a solvent molecule bonds to the boron atom while hydride is being transferred to the carbonyl compound. Another solvent molecule (if the solvent is protic) provides the proton for the carbonyl oxygen that has the electrons from the broken π-bond. Therefore, while the overall reduction of carbonyl requires two hydrogens, only one of these comes from the reagent (that on carbon); the other hydrogen comes from the protic solvent. Sodium Borohydride and Lithium Aluminum Hydride Reduction Reaction

MeOH

Cyclohexanone

Cyclohexanol

In this equation 1 mole of sodium borohydride or lithium aluminum hydride can reduce 4 moles of an aldehyde or ketone! However, in practice, it is best to use a 50-100% excess of the reducing agent. Acidified water is added to the reaction after the reduction is complete to decompose the excess reducing agent and to provide protons for the neutralization of the product if the reaction solvent was aprotic. Reaction Conditions The reaction solvent for a sodium borohydride reduction is usually an alcohol (methanol, ethanol or isopropanol) or a dilute aqueous NaOH solution (≤1M). Sodium borohydride decomposes rapidly in low pH and even neutral aqueous solutions. Even acidic functional groups such as carboxylic acids and phenolic OH groups can cause decomposition of borohydride. These functional groups are best neutralized (with NaOH) before NaBH4 is added to the reaction. Sodium borohydride reacts more slowly with alcohols, making these suitable solvents when no acidic functional groups are present. The reaction is usually performed by dissolving the carbonyl compound in the reaction solvent, and carefully adding a solution of the reducing agent. The borohydride solution is added slowly enough not to raise the reaction temperature above 25C, and the reaction is cooled if necessary. Higher temperatures may cause the borohydride to decompose too quickly. Some carbonyl compounds need to have longer reaction times and/or higher reaction temperatures in order to be reduced completely. The carbonyl compounds that need longer reaction times or higher reaction temperatures are either aromatic ketones or particularly sterically hindered ketones. Sodium borohydride has a molecular weight of 38. It therefore has massive molar reducing power relative

CYCLOHEXANOL

EXPERIMENT #4

to its molecular weight. Coincidentally, lithium aluminum hydride also has a molecular weight of 38 and therefore has similar reducing power. The principal difference between these two reagents is that an aluminum-hydrogen bond is far more reactive than a boron-hydrogen bond; it will react violently with water and other hydroxylic solvents to generate H 2(gas). For this reason, lithium aluminum hydride can be utilized only in aprotic solvents, such as ether, and in anhydrous environments. LiAlH4 is also expensive and somewhat dangerous to use. Sodium borohydride, because it is a mild reducing agent, is relatively safe and can be used in aqueous or alcoholic solvents, such as water, ethanol, methanol or propanol. Solid NaBH4 will decompose slowly when in contact with moist air, so the container should always be tightly closed when NaBH 4 is not being removed. Hydrogen in the presence of metal catalyst (such as Na metal) reduces compounds in the same manner as lithium aluminum hydride, however hydrogen reduces alkenes and alkynes in addition to carbonyl compounds and nitriles Tips: - Explicitly state which reducing agent you intend to use and give a rational for your choice in your proposal - The reducing agent should be in a 100% excess when compared to the desired moles of your product. - Methanol will be present if your reaction volume is too small to be used effectively. - There will be no catalysts available. - Ice will be present and it is important to keep reduction reactions chilled to avoid losing volatile reagents. - You should stir the solution for at least 10 minutes to ensure that the reduction reaction is complete. - Hydrochloric acid will be available to decompose excess reducing agent. - Parafilm will be available to store your reduced product until the next laboratory session. - After the reduction reaction you will want to purify your product. This should be done on the second laboratory session. Please explain in your proposal how you intend to purify the cyclohexanol. - Do not forget to measure the amount of product that you produce and determine the purity of your product. The method(s) that you use to determine purity should be part of your proposal. Relevant Appendix Sections A2 – Glassware B2 – Refractive Index Determination B3 – Infrared Spectroscopy C4 – Separation of Liquids by Distillation C5 – Extraction D – Common Calculations For your Proposal: This should be short, but include a detailed procedure that includes the amounts of each reagent used, the glassware required. You will also need to explain your choice of how to make the cyclohexanol and include a cost analysis. Please ensure that you have all of the pertinent physical data for both reagents and products. You do not need to know the melting point of sulphuric acid. Calculations should appear as an appendix to your proposal. Take note of the due date for the proposal.

CYCLOHEXANOL

EXPERIMENT #4

SAFETY It is highly recommended that you consult all of the relevant SDS sheets prior to entering the lab. Below are the chemicals that will be available and the WHMIS 2015 pictograms. You will not need all of these chemicals, and all of them are clear colourless liquids, so please label all glassware appropriately. Cyclohexene

Sulphuric Acid

Cyclohexanone

Sodium Borohydride

Methanol

HCl

Potassium Carbonate

Sodium Chlroide

Cyclohexanol...