Synthesis of Esters Lab Report

Synthesis of Esters Lab Introduction The purpose of this experiment was to synthesize four different esters and identify them by smelling their specific odours. The hydroxyl group, , is the functional group of alcohols, which is a hydrogen bonded with an oxygen that is covalently bonded to the remainder of the molecule. Carboxylic acids are organic chemicals with a carboxyl functional group, , at the end of their carbon chain, and they can be prepared by the oxidation of aldehydes. An esterification reaction is a condensation reaction in which a carboxylic acid and an alcohol combine to produce an ester and water (Van Kessel et al, 2003). Esters are organic chemicals that contain an ester linkage, , and are formed when an alcohol and an organic acid react together. The human olfactory glands, commonly referred to as Bowman’s Glands, are in the mucous membrane of the olfactory part of the human nasal cavity. Human olfactory glands produce mucus in order to moisten the olfactory epithelium and dissolve substances that produce odours. (Wikimedia Foundation, 2018) There were fourteen chemicals used to conduct this experiment. The three alcohols used during this experiment were ethanol (C2H5OH), methanol (CH3OH), and 3-methylbutan-1-ol (C5H12O). Ethanol is a colourless, transparent, viscous liquid with a molar mass of 46.070 g/mol. Methanol is a colourless, transparent, viscous liquid with a molar mass of 32.042 g/mol. 3-methylbutan-1-ol is a colourless, viscous, oily, transparent liquid with a molar mass of 88.150 g/mol. The six acids used during this experiment were butanoic acid (C4H8O2), decanoic acid (C10H20O2), salicylic acid (C7H6O3), benzoic acid (C7H6O2), ethanoic acid (CH3COOH), and sulphuric acid (H2SO4). Butanoic acid is a colourless, transparent, viscous, liquid with a molar mass of 88.110 g/mol. Decanoic acid is a white, opaque, solid powder with a molar mass of 172.260 g/mol. Salicylic acid is a white, opaque, solid powder with a molar mass of 138.121 g/mol. Benzoic acid is a translucent, white-hued, crystal-like solid with a molar mass of 122.120 g/mol. Ethanoic acid is a colourless, transparent, viscous, liquid with a molar mass of 60.050 g/mol. Sulphuric acid is a colourless, transparent, viscous, liquid with a molar mass of 98.079 g/mol. The five esters created as products during this experiment were ethyl butanoate (C6H12O2), ethyl decanoate (C12H24O2), methyl salicylate (C8H8O3), methyl benzoate (C8H8O2), and 3-methylbutyl ethanoate (C7H14O2). Ethyl butanoate is a colourless, transparent, viscous liquid that has a fruit-like odour and a molar mass of 116.160 g/mol. Ethyl decanoate is a viscous, oily liquid with a wax-like, apple-like scent and a molar mass of 200.322 g/mol. Methyl salicylate is a colourless, viscous, oily liquid with a mint-like odour and a molar mass of 152.149 g/mol. Methyl benzoate is a colourless, viscous, oily liquid with a pleasant, fruit-like scent and a molar mass of 136.150 g/mol. 3-methylbutyl ethanoate is a colourless, transparent, viscous, oily liquid with a banana-like odour and a molar mass of 130.185 g/mol. 2 Procedure To prepare for the experiment, four test tubes, a test tube rack, a 1L beaker, a 100mL beaker, a watch glass, a hot plate, a thermometer, and a petri dish were collected. The test tubes were labelled numbers 1 to 4, in order to keep track of them. 1mL of ethanol, 1 mL of butanoic acid, and 4 drops of sulphuric acid were added to the first test tube. 1mL of ethanol, 1 scoop of decanoic acid, and four drops of sulphuric acid were added to the second test tube. 1mL of methanol, 1 scoop of salicylic acid, and 4 drops of sulphuric acid were added to the third test tube. 1mL of methanol, 1 scoop of benzoic acid, and 4 drops of sulphuric acid were added to the fourth test tube. The test tubes were placed in order in the test tube rack. The 1L beaker was filled with water and placed onto the hot plate. The hot plate was turned on and the water was heated to 60oC. The temperature of the water was measured using the thermometer. Once the water had heated up to 60oC, all four test tubes were placed into the water for five minutes. After the five minutes had passed, the four test tubes were removed from the water inside of the 1L beaker. The petri dish was then filled with cold water and the contents of the first test tube were poured into the dish. The contents of the petri dish were wafted, and the odour of the contents were smelled and recorded. This was done for each of the test tubes. Then, 1mL of 3-methylbutan-1-ol, 1mL of anhydrous ethanoic acid, and four drops of sulphuric acid were added into the 100mL beaker. The watch glass was quickly placed over the top of the beaker, covering its opening. After it had been determined that the contents in the 100mL beaker had sufficiently reacted, the watch glass was removed from the opening of the beaker. The contents of the 100mL beaker were wafted, and the odour was smelled and recorded. Results Table 1: The Odours of the Reactants in the Experiment Reactant Name Ethanol Methanol 3-methylbutan-1-ol Butanoic Acid Decanoic Acid Salicylic Acid Benzoic Acid Ethanoic Acid Odour of Reactant Vinous Slightly Alcoholic Unpleasant Old Cheese Rancid Odourless Faint, Pleasant Pungent Table 2: The Odours of the Products in the Experiment Product Name Ethyl butanoate Ethyl decanoate Methyl salicylate Methyl benzoate 3-methylbutyl ethanoate Odour of Product Fruity, Pineapple-like Waxy Minty, Spearmint-like Fruity Banana 3 Discussion Sulphuric acid (H2SO4) and heat were used as the catalysts during the reactions in this experiment. Q1 As previously mentioned, an esterification reaction is a condensation reaction in which a carboxylic acid and an alcohol combine to produce an ester and water (Van Kessel et al, 2003). Q2 In an esterification reaction, the hydrogen ion from the sulphuric acid is transferred to the carboxylic acid, becoming attached to the acid’s double bonded oxygen. Q2 This hydrogen ion transfer gives the hydrogen ion a slightly positive charge, as well as giving both the oxygen and carbon atoms a slightly positive charge. Q2 The positive charge of the carbon atom is then ‘attacked’ by one of the the alcohol’s oxygen atoms, and a water molecule is then taken from the ion. Q2 The hydrogen ion is then taken from the oxygen by reacting with a hydrogen sulphate ion that was formed during the beginning of the reaction. Q2 At the end of an esterification reaction, an ester is formed and the catalyst is regenerated. (Farmer, 2014) Q2 The five reactions that occurred during this experiment are: Q3-4 The odour that is expected for the chemical ethyl butanoate is similar to that of pineapple. The odour that was smelled during the experiment was fruity, like pineapple. Q5 The expected odour of the chemical ethyl decanoate is wax-like, and during this experiment, it was found that there was no distinguishable odour to be smelled. Q5 The odour that is expected for the chemical methyl salicylate is wintergreen, and during this experiment it was determined that the methyl 4 salicylate smelled like spearmint. Q5 The expected odour of the chemical methyl benzoate is fruity, however, during the experiment it was found that the methyl benzoate smelled like mint. Q5 The odour that is expected for the chemical 3-methylbutyl ethanoate is banana-like, and this was found to be true during the experiment. (Kennedy, 2013) Q5 Esters such as ethyl formate, N-amyl acetate, and methyl butrate can be found in common foods and beverages that humans consume. Q6 The ester ethyl formate (C3H6O2) is found in raspberries, giving them their flavor, and it can also be found in other food and drink substances including fruits, coffee, tea, and grains. Q6 Ethyl formate is commonly used as a flavoring agent in artificial beverages and lemonade, and it is also used in processed foods such as dried fruits and cereals. (American Chemical Society, 2018) Q6 N-amyl acetate (C7H14O2) is an ester that can be naturally found in fruits such as pears and bananas, and can be used as a flavor ingredient (Sigma-Aldrich, n.d). Q6 The ester methyl butanoate (C5H10O2) is present in many plant products, especially pineapple oil, and it can be produced by the distillation from essential oils of vegetable origin (Robert A. Flath, 1970). Q6 Potential experimental errors could include imprecise measurements of the alcohol and carboxylic acid that were being added to the beaker. Also, the temperature of the water in the 1L beaker did not remain at exactly at 60oC for the duration of the test tubes being inside of it, and it went from as low as 55oC up to as high as 65oC. The temperature could have increased or decreased the rate of reaction happening in each test tube. Although there were experimental errors made, they would not affect the results gathered from the experiment itself.