Question

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 –6.3 ^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 “brisk” 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 “water-insoluble”.

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 –

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 – 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.