01:160:311 Lecture Notes - Lecture 7: Azeotropic Distillation, Le Chatelier'S Principle, Butyl Acetate

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16 Nov 2018

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Use le chatelier"s principle in 2 ways: Dry with molecular sieves - cannot use other drying agents such as na2so4 or. Cacl2 because they do not remove water at the temperature at which esters are formed. Remove h2o via azeotropic distillation: bp of azeotrope mimics bp of pure compound (stays constant) Because boiling points of acetic acid, 1-butanol and butyl acetate are very close, an excess of starting material would be significant impurity to the product. How le chatelier"s priciple could be used to promote transesterification to use le chatelier"s principle to move reaction forward, the alcohol on the reactant side can also be used as a solvent. Why are simple and fractional distillation not suitable for separating product from reactants if excess reactant used in synthesis of n-butylacetate. Cannot use simple/fractional distillation boiling point difference of 9 c is too small and for fractional distillation, hold up can cause product to be lost.

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Can anyone tell me how to get the percent and theoretical yield here?

- 2129 11 W- CH 4521-6: Fischer Esterification Introduction Esters are among the most widespread of all naturaly liquids that are responsible for the pleasant odors of fruits and flowers. Examples are ethyl cinnamate, whic occurring.compounds. Many simple esters are fragrant Ts the smell of cinnamon, and isobutyl acetate, contributing to the aroma of cherries, raspberries and of giycerol and fatty acids Esters are characterized by having the functional group:RO.R,where Escher esterification. This reaction refluxes a carboxylic acid inan . However, the most common esters found in nature are fats and ble oils, which are esters a carbon is double-bonded to one alcohol, creating the ester plus water as oxygen atom and sin The most classic method for creating an ester is the products: estor orer alcohai +R-OH catalyst A strong acid, traditionally sulfurits acid, is used as a catalst. Since the reaction is at equilbrium, simply reacting one mole of asid with one mole of alcohol will give a mixnture of starting materals and yield of the product may be improved using le Chatelier's principle: . Using the alcohol as a solvent (le. arge excess wil hlp push the equllbrium to the right By sequestering water (a reaction product), the equilibrium is pushed to the right. The use of a solvent which forms low-bolling azeatropes with water, such as toluene, in conjunction with a Dean-Stark apparatus has a similar effect, as is the use of other drying agents like molecular sieves Since low molecular weight esters typically have lower boling points than their parent carboxylic acids and alcohols because they are not able to form hydrogen bonds, the ester products may be distilled out of the reaction vessel as they are formed. By removing the ester product in a reactive distillation, the equilibrium once again lies to the righ For today's experiment, you will be able to choose which sweet-smelling ester you want to make. The table of reactants below gives you an idea of the range of smells. An ester will esterification reaction. This reaction involves mixing an alcohol with a carboxylic acid to form an ester and water. The reaction is reversible and an example is shown below be synthesized using the Fischer catalyst acetc acid propanopropyl acetate (pear) 47

Please help me with the following problem. It has many parts to it, but it is one question. Thank you in advance

Synthesis of 1-Bromobutane

Reaction Scheme

NaBr, H2SO4

CH3CH2CH2CH2OH---------------------> CH3CH2CH2CH2Br + NaHSO4 + H2O

H2O

Possible by-products:

1-butene (bp â6.3 ^oC), di-n-butyl ether, C₄H₉OC₄H₉, (bp 141 ^oC)

Properties of reagents and product:

Substance	Mol Wt. (g/mol)	Density (g/ml)	bp, ^oC	Solubility	Hazards
1-butanol	74.12	.81	117-118	Sol water, Miscible alc, ether, and more	Flammable, irritant
H₂SO₄ (con)	98.07	1.84	280	X	corrosive material
sodium bromide	102.89	X	X	X	X
1-bromobutane	137.03	1.27	101.6	Insol in water; sol in alcohol, ether	Flammable, irritant

Quantities used in the reaction and yield data:

Substance	g or mL	Calculated moles	Theoretical Yield moles grams		Actual Yield, grams
1-butanol	mLs		x	x	x
H₂SO₄ (con)	11.5 mL		x	x	x
sodium bromide	13.3 g		x	x	x
Water	15.0 mL	x	x	x	x
1-bromobutane	x	x			Want 7.5 g

A. Assume the above synthesis of 1-bromobutane is known to proceed in 75% yield and you would like to prepare 7.5 g of material. Back calculate how many mLs of 1-butanol you will need for the reaction to synthesize the 7.5 g of product, assuming that the 1-butanol is the limiting reagent. Place this number in the table. Also, calculate all the remaining missing data to fill the table.

Experimental Procedure: The NaBr, 1-butanol, and water are combined in a round-bottomed flask containing a stir bar and cooled to 0 ^oC. Concentrated sulfuric acid is slowly added with stirring. The reaction flask is then prepared for a 50-minute âbriskâ reflux using a heating mantle. After reflux, two layers will be present. The condenser is removed and replaced with a distillation apparatus. Distill the mixture, recording the temperature range, until no more water- insoluble droplets are collected and the temperatures reaches around 115 ^oC. (The boiling point is elevated due to azeotropic distillation of the water with the 1-bromobutane and increasing amounts of sulfuric acid).

B. Propose a way that you could test if the droplets coming over are âwater-insolubleâ.

Be specific with the manipulations, glassware, and what observation you would see.

The collected liquid is transferred to a separatory funnel and 10 mL of water is added. Two layers form, the bottom being the 1-bromobutane layer. The layers are separated, one through the bottom and one through the top, and the separatory funnel is cleaned and dried. The bromobutane layer is returned to the separatory funnel and washed with ice-cold sulfuric acid to remove traces of the starting material, butene and ethereal by-products.

C. Will the top or bottom layer be the bromobutane layer when washing with concentrated sulfuric acid? Why?

The sulfuric acid layer is removed and the 1-bromobutane is washed with 10 mL 3 M NaOH followed by 10 mL aqueous sodium chloride (brine).

D. What is the purpose of each of these washes?

NaOH â

Brine -

Care should be taken to save the correct layer. The 1-bromobutane is then dried over anhydrous CaCl₂.

E. How will you decide how much drying agent to use? How will you know that the 1-bromobutane is dry.

The product is distilled to obtain a clear, colorless liquid.

F. TLC â Suppose you wanted to follow the above reaction by TLC.

a. Describe how you would go about finding a good solvent or solvent pair to use.

b. Suggest a specific solvent system you would try.

c. Draw below what you would want the TLC plate to look like and show the expected relative R_f values for the 1-butanol and 1-bromobutane. Label the spots, baseline, and solvent front.

01:160:311 Lecture Notes - Lecture 7: Azeotropic Distillation, Le Chatelier'S Principle, Butyl Acetate

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