Name: Anna Dempniak Date: Wednesday 13 th 2018 Teacher: McGuckin Course code: SCH4UP. The Preparation of Esters

Transcription

1 Name: Anna Dempniak Date: Wednesday 13 th 2018 Teacher: McGuckin Course code: SCH4UP The Preparation of Esters

2 Dempniak 2 Abstract The purpose of this lab was to observe the scents of six different esters. Esters were formed during the experiment by combining sulfuric acid, one of six alcohols, and one of four carboxylic acids in a test tube. The test tube was heated in a water bath on a hot plate to speed up the reaction, then mixed with distilled water and left to cool in ice water. This process was repeated six times with different alcohols and carboxylic acids resulting in six test tubes each containing a different type of ester. Each test tube was smelled and its scent was compared to the anticipated scent (based on the ester product of the predicted reaction). Test tubes three and six matched the predicted scent, while test tubes one and four kept some aspects of their predicted scent. Test tubes two and five held no trace of the predicted smell. Introduction Although most people are unaware of their existence, esters are one of the key pillars that make up life. Ester bonds can be found everywhere from the fat that makes up your leg to the phosphodiester backbone that forms DNA to the fragrant smell coming off an orange. (Pure Chemicals 2018) So what exactly is an ester? An ester is an organic compound containing at least two carbon chains and two oxygen atoms. The carbon chains must be connected to each other by one of the oxygen atoms, and one of the connecting carbon atoms must be double-bonded to the other oxygen atom.(bbc, 2014) Typically esters are created through a condensation reaction called esterfication. In esterfication, an organic compound containing a -OH group (an alcohol) is combined with an organic compound containing a -COOH group (a carboxylic acid). (BBC, 2014) The two hydrogen atoms from the two hydroxide groups in each compound pair with one of the oxygens from the hydroxide groups to form water, leaving the former alcohol and carboxylic acid connected by the remaining oxygen. One thing that esters are famous for is their unique odours and fragrances. Esters usually contain weak intermolecular forces which allows ester molecules to easily become gaseous and thus inhaled. (Dissenter 2014) Esters are responsible for the smells in many common fruits and plants, ranging from bananas to mint. (The Editors of Encyclopaedia Britannica, 2018) For example the ester Pentyl acetate smells like apples while Propyl acetace smells like pears. Esters include a whole range of easily available flavors: Methyl Salicylate smells minty, Ethyl butyrate has a pineapple scent, Isobutyl formate is described ethereal and slightly fruity, and Octyl acetate is the ester that gives oranges their

3 scent. (Pub Chem, 2018) Each combination of different carboxylic acid and alcohol results in a Dempniak 3 different ester with its own unique smell hence many different fragrances can be created using esters. Purpose The purpose of this lab was to observe the scent of six different esters by combing the necessary alcohol and carboxylic acid. Materials and Equipment 6 test tubes 1 mlmethanol pencil 1 ml ethanol Test tube rack 1 ml isobutyl alcohol Eyedropper 1 ml 2-methylpropanol (isobutyl alcohol) Scale 1 ml1-octanol 2 x 250 ml beakers 3 ml Glacial acetic acid 10mL graduated cylinder 1 ml Formic Acid Thermometer 1 ml Salicylic acid Safety googles 1 ml Butanoic acid Concentrated sulfuric acid 1mL 1-propanol 1-pentanol Procedure 1. Test tubes were labelled with the numbers one to six using pencil ml of tap water in a 250mL beaker was heated on hot plate to 60 C. 3. Alcohols were added to test tubes as follows:1 ml of 1-pentanol was added to test tube one, 1 ml of 1-propanol was added to test tube two, 1 ml of methanol was added to test tube three, 1 ml of ethanol was added to test tube four, 1 ml of isobutyl alcohol was added to test tube five, and 1 ml of 1-octanol was added to test tube six. 4. Four drops of sulphuric acid was added to each test tube. 5. One gram of salicyclic acid was weighed on scale. 6. Acids were added to test tubes as follows:1 ml of acetic acid was added to test tube one, two and six, 1 g of salicyclic acid was added to test tube three, 1 ml of butanoic acid was added to test tube four, and 1 ml of formic acid was added to test tube five.

4 7. Test tubes were heated in prepared beaker of hot water for fifteen minutes. 8. Test tubes were taken off water bath cooled in a beaker of cold water ml of water was added to each of the test tubes. 10. Test tubes were wafted and sniffed individually. The smell of each test tube was recorded. Results Odour of Test Tubes after Procedure Test tube Name of Ester Formed Predicted Odour Odour 1 Pentyl acetate Bananas/apples Slightly fruity with chemical smell Dempniak 4 2 Propyl acetate Pears Smells like nail polish remover 3 Methyl Salicylate Sweet, wintergreen Minty 4 Ethyl butyrate Pineapple Slightly fruity possibly apple smell with chemical smell 5 Isobutyl formate Ethereal, slightly fruity Smells like paint thinner 6 Octyl acetate Orange flavour Orange candy flavor Balanced Equations Test Tube 1 : Formation of Pentyl Acetate CH 3 COOH + C 5 H 12 O C 7 H 14 O 2 + H 2 O Test Tube 2 : Formation of Propyl Acetace CH 3 COOH + C 3 H 8 O C 5 H 10 O 2 + H 2 O Test Tube 3 : Formation of Methyl Salicylate C 7 H 6 O 3 + CH 3 OH C 8 H 8 O 3 + H 2 O Test Tube 4 : Formation of Ethyl Butyrate C 4 H 8 O 2 + C 2 H 6 O C 6 H 12 O 2 + H 2 O Test Tube 5 : Formation of Isobutyl formate CH 2 O 2 + C 4 H 10 O C 5 H 10 O 2 + H 2 O Test Tube 6 : Formation of Octyl acetate CH 3 COOH + C 8 H 18 O C 10 H 20 O 2 + H 2 O

5 Dempniak 5 Discussion Esters are a group of organic compounds noted for their wide range of odours and flavors. Since esters are created by mixing a carboxylic acid and an alcohol it is possible to synthesize a specific scent by combining the right carboxylic acid and alcohol. (The Editors of Encyclopaedia Britannica, 2018) This experiment attempted to create six different scents using four different carboxylic acids and six different alcohols. Pentyl acetate, which is known for its apple flavor, was formed using pentanol and acetic acid. Propyl acetate, known for a pear scent, was created from propanol and acetic acid. Likewise methyl salicylate (wintergreen scent) was formed from methanol and salicyclic acid, and ethyl butyrate (pineapple scent) was made from ethanol and butanoic acid. Octyl acetate (orange smell) was made from octanol and acetic acid. Finally isobutyl alcohol and formic acid were used to create isobutyl formate which was expected to have a fruity, ethereal smell. While the esters were relatively easy to synthesize in the laboratory, the majority of the esters formed did not give off the expected scent. Methyl salicyclate and Octyl acetate matched the predicted scent fairly closely. Pentyl acetate and ethyl burate smelled predominantly like chemicals but contained a slight fruity scent though it was hard to tell what fruit it was. Isobutyl formate and propyl acetate did not smell remotely ethereal or pear-like but smelled like paint thinner. The discrepancies between the predicted results and the observed results could be for a number of reasons. For one, throughout the entire experiment the fume-hood ran, ventilating the carboxylic acids. This spread a distinct chemical scent around the room which likely interfered with the smells of the esters even when they were taken outside to be tested. Secondly, during the experiment it was hard to come up with the correct words to describe smells and two people could describe the same smell somewhat differently. Compared to sight or sound, smell is a less objective sense. Anyone can tell if a chemical turns green, and it is easy to describe the visual difference. With smell however there is no set words to really describe smells except by comparing them to other scents or using vague words. For example isobutyl formate is described as an ethereal scent, ethereal being defined as delicate in a way that seems too perfect for this world (Merriam Webster, 2018). This description does not set down any clear guidelines as what someone considers delicate and perfect scent completely changes depending on the person. It is possible that although a particular scent may be deemed to have an apple flavor in this experiment, another experimenter might consider that flavor more of a pear scent. Finally, during the experiment no time was set aside for the experimenters nose to clear in between smelling test

6 Dempniak 6 tubes. When comparing flavors of cheese or wine usually there is some kind of palate cleanser in between samples so that the flavor of the last sample does not affect the flavor of the next. It is possible that since there was no time for the nose s palate to clear, the previous test tube s scent affected the next test tube s perceived scent. Although these sources of error could explain smaller discrepancies in scents theycannot account for the huge discrepancy between a fruity ethereal smell and the smell of paint thinner. Possibly the esters were not diluted enough and as a result the smells came across too strong. In order to determine for certain why the scents were so off the mark, further experimentation or research would be necessary. Despite the failure of this particular experiment to produce predictable and useful scents, esterfication has many uses in industry. Parabens, a type of ester that inhibits the growth of moulds and yeast, is used as a preservative in food and drugs.(pure Chemicals 2018) Manufacturers use esters with pleasant odours as ingredients in perfumes, as food flavourings that improve the smell and taste of processed food. Esters can be added to essential oils, cosmetics, and more to enhance their appeal to the consumer. (Pure Chemicals 2018) As its name suggests, esters are necessary to the manufacturing of polyester. Conclusion This experiment, although it did successfully form esters in all the test tubes, did not produce the expected smell in test tubes two and five. The reason for this discrepancy requires further experimentation or research before making any strong conclusions.

7 Dempniak 7 References Admin. (2015, September 9). Esters: Its Chemical Nature, Properties and Uses. Retrieved June 14, 2018, from Pure Chemicals website: Carboxylic acids and esters. (2014). Retrieved June 14, 2018, from BBC website: _acids_esters/revision/5/ Clark, J. (2014). Introducing esters. Retrieved June 14, 2018, from Dissenter, J. (2014, February). Why do esters actually smell? Retrieved June 14, 2018, from The Editors of Encyclopaedia Britannica. (2018). Ester. Retrieved June 14, 2018, from Ethereal. (2018, June 15). Retrieved June 14, 2018, from Merriam Webster website: Isobutyl Formate. (n.d.). Retrieved June 14, 2018, from Pub Chem website: