Week 6 Acids, Esters and Amides Workbook - Monash

8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Week 6: Acids, esters and amides - workbook Site: Monash Moodle1 Printed by: Ka...

8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Week 6: Acids, esters and amides - workbook Site: Monash Moodle1 Printed by: Kaltham Alzaabi Unit: CHM1022 - Chemistry II - S2 2024 Date: Monday, 26 August 2024, 1:50 PM Book: Week 6: Acids, esters and amides - workbook https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 1/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Table of contents 1. Pre-workshop material 1.1. Carboxylic Acids 1.2. Esters 1.3. Amides 1.4. Reactions 1.5. Applications 2. Summary 3. Preparation quiz 4. Online lectures 5. Workshops https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 2/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1. Pre-workshop material The Carbonyl Group The carbonyl group is common to several classes of organic compounds which are distinguished according to what is bonded to the carbonyl (Figure 1). An aldehyde consists of a carbonyl centre bonded to a hydrogen and an R group (any hydrocarbon substituent). A ketone consists of a carbonyl centre bonded to two hydrocarbon groups. We will be focussing on the following three classes; carboxylic acids, esters and amides. A carboxylic acid has a hydrocarbon group and an alcohol attached to the carbonyl center (-OH). An ester is similar to this, however, the hydrogen of the acid is replaced by another alkyl group (-OR’). An amide consists of a carbonyl centre bonded to a hydrocarbon group and an amine (-NH2, -NHR’ or -NR2). Figure 1: Classes of carbonyl containing compounds Carboxylic acids, esters and amides are similar in structure. These structural similarities account for their similar properties. They all have higher boiling points in comparison to alkanes of similar size. Please read Sections 23.1-23.5 of Chemistry, Blackman et al. (4th ed.) Please read Chemistry: Atoms First (2019), Chapters 21.3-21.4 https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 3/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1.1. Carboxylic Acids Many carboxylic acids are colourless liquids with unpleasant odours. Carboxylic acids with 5 to 10 carbons have a characteristic “goaty” odour. These acids are also produced by the action of skin bacteria on human oils. Acids with an excess of 10 carbon atoms are wax like solids. Odour is diminished with increasing size due to the decrease in volatility. Carboxylic acids with 1 to 4 carbon atoms are miscible with water as the carbonyl is readily able to engage in hydrogen bonding with water. Solubility decreases with increasing carbon chain length because dipole forces become less predominant while dispersion forces become more predominant. Carboxylic acids exhibit strong hydrogen bonding between molecules and therefore exhibit high boiling points in comparison to compounds of comparable molar mass. Carboxylic acids are named according to the IUPAC system where the suffix (-e) is replaced with -oic acid (Figures 2). Figure 2: Various carboxylic acids Figure 3: Physical properties of various carboxylic acids Carboxylic acids are typically weak acids, meaning they partially dissociate to form H+ ions and RCOO- anions. Carboxylic acids establish equilibrium in aqueous solution with carboxylate anions (RCOO-). Acetic acid has a pKa of 4.76 in water, meaning that in a 1.0 M solution about 0.4% of the acid groups will be dissociated to form the carboxylate (Figure 4). https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 4/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Figure 4: Carboxylate anions https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 5/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1.2. Esters Esters are colourless and volatile liquids with pleasant odours. They have distinctive fruit-like odours and many occur naturally in essential oils of plants. Esters are derived from carboxylic acids. The -OH group of the carboxylic acids is converted to an -OR in an ester. This loss of the hydrogen in the molecule also leads to a loss in possibility for molecules to form hydrogen bonds in esters. Therefore, boiling points are not as high as boiling points of carboxylic acids. Small esters are fairly soluble in water but the solubility decreases with increasing chain length. Their slight solubility is attributed to the fact that although esters can’t form hydrogen bonds with themselves, they can form hydrogen bonds with water molecules. Esters consist of two words. The first is the name of the alkyl group R' of the ester group and it ends with -yl. The second is the name of the parent acid, with the family-name ending -ic acid replaced by -ate (Figure 7). Figure 7: Various esters https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 6/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1.3. Amides Compounds with a nitrogen directly attached to the carbonyl carbon atom are called amides. The nitrogen of an amide may be unsubstituted (- NH2), monosubstituted (-NRH) or disubstituted (-NR2). Amides are typically solids, with the exception of formamide (HCONH2) which is a liquid. Importantly, amides are not basic like amines. Amides with an unsubstituted —NH2 group are named by replacing the -ic acid or -oic acid of the corresponding carboxylic acid name with -amide. If the nitrogen atom has alkyl substituents on it, the compound is named by specifying the alkyl group and then identifying the amide name. The alkyl substituents are preceded by the letter N to identify them as being attached directly to nitrogen (Figure 8). Figure 8: Various amides https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 7/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1.4. Reactions Reactions of Carboxylic Acids Ester synthesis The conversion of carboxylic acids to esters using acid and alcohol is called the Fischer Esterification (Figure 11). The mechanism of this reaction will be discussed in the workshops. Figure 11: Ester formation Amide synthesis The amide bond is can be synthesised from a carboxylic acid and an amine. This reaction does not proceed easily, as the amine is a base and will deprotonate the acid (Figure 12). This inhibits amide bond formation, as the protonated amine is a poor nucleophile and the carboxylate anion is a poor electrophile. Heating to a high temperature (typically >160 °C) is required to form the amide product. Because of this poor reactivity, amides are usually made from activated acids. This will be discussed in the workshop. Figure 12: Amide bond formation Hydrolysis of esters and amides Esters and amides can be hydrolysed to yield back the parent carboxylic acid and corresponding alcohol or amine. The equilibrium of this reaction can be pushed towards the acid by adding an excess of water. The most well known hydrolysis reaction is saponofication, in which triglycerides (fats) are reacted with sodium hydroxide to yield fatty acids and glycerol. Soap is produced in this way. Figure 15: Reactivity series for acyl substituents Amides are considerably more stable than esters. While esters can be hydrolysed in acid or base catalysed reactions, amides only undergo hydrolysis in acid catalysed reactions. This difference in reactivity stems from the fact that -NH2 cannot be split of from the amide easily, while - NH3+ can leave the molecule and be replaced by an OH group. https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 8/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 The reactivity of carboxylic acids and their derivatives depends on the basic strength of the acyl-bound substituent. -NH2 groups are the most basic, followed by -OR and OH groups. https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 9/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 1.5. Applications Carboxylic acids in nature There are numerous examples of carboxylic acid, ester and amide containing groups in nature. In order to expose you to the breadth of compounds which contain these functional groups we will explore a few examples. Salicylic acid is an organic carboxylic acid which is derived from the metabolism of salicin which is produced in willow bark. Although salicylic acid displays its own pain relieving properties, its acidity is too high and can cause severe stomach pain when ingested. Esterification of salicylic acid with acetic anhydride yields acetyl salicylic acid (Aspirin) (Figure 1). Figure 1: Esterification of salicylic acid with acetic anhydride Source: picture alliance / dpa / dpa central image / Peter Endig Morphine, heroin and codeine are all examples of drugs from the opiate family (Figure 2). In a series of transformations, morphine is esterified with acetic acid to yield heroin. Codeine is another opiate in which the ester is replaced by an ether. It is obvious that all three compounds have different uses and effects on a human body. Yet, the chemical change is small, highlighting the importance of these variations in medicinal chemistry. Figure 2: Structures of morphine, heroin and codeine https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 10/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 2. Summary This week we have learnt about the properties of carboxylic acids and their derivatives. A key focus of this week has been on understanding the structure and electronics of carbonyl containing functional groups and how they react with nucleophiles. Explore the 3D representation for the nucleophilic substitution at a carbonyl group illustrated in this ChemTube 3D page (click the link). Use the controls located at the right hand corner of the image of the molecule to rotate it. Click on each of the molecular structures/reaction arrows to load the corresponding 3D representations, and see the animations. https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 11/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 3. Preparation quiz Now that you have completed the pre-workshop material, attempt the following preparation quiz. These 10 questions give you a chance to test your knowledge and practice the skills that were covered in this week's pre-workshop material. This material is essential for this week's workshops and may be applied in your laboratory classes. You have two attempts at each quiz and your highest attempt will count towards your final grade. Preparation quiz for Week 6 https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 12/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 4. Online lectures Week6-L1-part1 These captions have been automatically generated. As such, the Week6-L1-part1 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up Week6-L1-part2 Week6-L1-part3 These captions have been automatically generated. As such, the Week6-L1-part3 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up Week6-L1-part4 These captions have been automatically generated. As such, the Week6-L1-part4 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 13/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Week6-L1-part5 Week6-L1-part6 These captions have been automatically generated. As such, the Week6-L1-part6 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up Week6-L2-part1 These captions have been automatically generated. As such, the Week6-L2-part1 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up Week6-L2-part2 https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 14/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 Week6-L2-part3 Week6-L2-part4 These captions have been automatically generated. As such, the Week6-L2-part4 quality is not 100% accurate. Accuracy may be affected by audio quality, topic under discussion and clarity of the speakers. Staff are not expected or required to edit or correct automatically- generated captions. It is best to not rely solely on captions when viewing video play_arrow content and to use them alongside other learning resources. Students who are registered with Disability Support Services should be in contact with them to discuss captioning if needed. Powered by Panopto get_app closed_caption fullscreen keyboard_arrow_up Online lecture slides can be downloaded from this link: Week 6 Lecture slides https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 15/16 8/26/24, 1:50 PM Week 6: Acids, esters and amides - workbook | MonashELMS1 5. Workshops Week 6 worksheet https://learning.monash.edu/mod/book/tool/print/index.php?id=2780608 16/16