che31expt-9

Name: Jobel D. De Pedro Group #: 6

Date Performed: Date Submitted:

Experiment 9 ACYL COMPOUNDS: SOAPS AND DETERGENTS I. OBJECTIVES 1. 2. 3. 4.

To observe observe the general properties of carboxylic acids. To compare the acidity of carboxylic acids and phenols. To verify experimentally experimental ly the interconversi interconversion on among acyl compounds. To become familiar familia r with the physical and chemical properties of fats and oils and to understand the chemical basis of these properties. 5. To learn how to prepare soap. 6. To compare the properties of soap and synthetic detergents. II. THEORETICAL FRAMEWORK Soap is an anionic surfactant used in conjunction with water for washing and cleaning that historically comes in solid bars but also in the form of a thick liquid. Soap, consisting of  sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol. Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture. Soaps are useful for cleaning because soap molecules attach readily to both nonpolar  molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Applied to a siled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water. (Fatty end):CH3-(CH2)n - COONa: (water soluble end) The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification. The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye, while some soapers use the historical hot process. Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali ( superfatting ), ), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap, though if too much fat is added it can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.

III. DATA AND RESULTS Table 1. Solubility and acidity of Carboxylic acids SAMPLE Acetic acid Benzoic acid Sodium benzoate

WATER WATER SOLUBILITY Soluble Insoluble Soluble

RXN TO LITMUS PAPER TEST Acidic: turns blue LP to red Acidic: turns blue LP to red Basic: no change in blue LP

Table 2. Relative acidities of Carboxylic acids and Phenols SAMPLE Phenol Benzoic acid

Solubility in 10% NaOH Soluble Soluble

Solubility in 10% NaHCO 3 Soluble Insoluble

Table 3. Observations upon addition of water and heating the samples, as well as their  reactions to litmus paper test. test . SAMPLE Acetyl Chloride Acetic anhydride Benzamide

RXN SIGNS Heat; semi-cloudy; bubble formation Clear, homogeneous solution Insoluble

WATER BATH No change No change Dissolved, clear solution

Table 4. Comparison of Soaps and Detergents

Hydrolysis Rxn with Acid Rxn with Soft Water  Rxn with Hard Water  Emulsifying Action

SOAP Cloudy, basic Turbid Turbid Formation of scums Formation of smaller bubbles

DETERGENT Clear, basic Clear  Clear  Turbid, no scums More bubbles were formed

IV. DISCUSSION Solubility and Acidity of Carboxylic Acids For table 1, Acetic acid and sodium benzoate were both soluble in water while benzoic acid was not. Unlike aldehydes and ketones, instead of protonation to be undergone to yield an alcohol, the initially formed alkoxide intermediate expels one of the substituents originally bonded to the carbonyl carbon, leading to the formation of a new carbonyl compound by a nucleophilic acyl substitution reaction. The different behavior towards nucleophiles of carboxylic acids derivatives is a consequence of structure. In the case of benzoic acid, the C=O carbon is electron-rich making the compound less ready to react with water, a nucleophile. The more electron-poor the C=O carbon, the more readily the compound reacts with nucleophiles. This is why acetic acid and sodium benzoate were able to dissolve in water. In table 2, both phenol and benzoic acid were soluble in 10% NaOH and were both insoluble in 10% NaHCO 3. Because acid dissociation is an equilibrium process, anything that stabilizes the carboxylate ion favors increased dissociation and increased acidity. Phenols and carboxylic acids are much more acidic than alcohols. In fact, some nitro-substituted phenols

even approach or surpass the acidity of carboxylic acids. One practical consequence of their  acidity is that phenols and carboxylic acids are soluble in dilute aqueous NaOH but remain undissolved in NaHCO 3. Hydrolysis of Acyl Compounds Acyl compounds differ in their reactivities toward nucleophilic acyl substitution and this is evident from their hydrolysis reactions. Hydrolysis is a chemical reaction in which compound is broken down by reaction with water. Acid halides are among the most reactive of the various carboxylic acid derivatives and can be converted into many other kinds of substances. The halogen can be replaced by the ±OH to yield an acid, by ±OR to yield an ester or by ±NH 2 to yield an amide. The table below shows the different observations upon addition of water and heating the samples, as well as their reactions to litmus paper test. Acetyl chloride, an acid chloride, was the first sample to react with water to yield carboxylic acids by the substitution of ±Cl by ±OH. The chemistry of acid anhydrides is similar to that of acid chlorides. Thus, results showed that acetic anhydride reacted with water to form acids, after heating. The ease of which the leaving group is lost depends upon its basicity: the weaker the base, the better the leaving group. For acid and anhydrides, the leaving group is the very weak base Cl- and CH3 respectively. Benzamide, an amide, is less reactive than acid chlorides and acid anhydrides. Amides undergo hydrolysis to yield carboxylic acids plus amine on heating in either aqueous acid or  base. Although the reaction is slow and requires prolonged heating, the overall transformation is a typical nucleophilic acyl substitution of ±OH for ±NH2. Saponification of Coconut Oil Triglycedrides are tri-esters of glycerol. They are the most naturally occurring occurring fats and oils. Alkaline hydrolysis of the three-ester linkages can break down triglycerides into their  component parts and yield long-chain carboxylate salts and glycerol. The hydrolysis of fats and oil (coconut oil, in this experiment) in a basic medium is commonly called saponification and the sodium salts produced are called soaps. Coconut oil is a source of lauric acid (12 carbons) which can be made into sodium laurate. Comparison of Soaps and Detergents Soaps and detergents are similar in their general structure and properties, but different in their composition and some specific properties. This was apparent their hydrolysis reactions, ability to react with mineral acids behavior in ³soft´ and ³hard´ water, and emulsifying properties were studied. Table 4 shows the results of the experiment. Soap from triacylglycerols is a mixture of long chain carboxylate salts. Detergents, on the other  hand, are amphiphatic and are generally characterized by the presence of a sulfonate group. It is a cleansing substance that acts similarly to soap but is made from chemical compounds rather than fats and lye. Soaps are the sodium salts of fatty acids. They are water soluble but the fatty acids themselves are not. Soap can be converted into the fatty acid by means of a reaction with a strong mineral (non-organic) acid. Acidification of detergents, on the other hand, produces acids which are often water soluble. Because of this, soaps are ineffective in acidic water. Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts such as calcium and magnesium as well as iron and manganese. Soaps react with metal ions in the water to form insoluble precipitates. The precipitates can be seen in the soapy water and are referred to as

³soap scum´. Unlike soaps, though, sulfonate in detergents does not form precipitates with the metal ions of hard water, reducing the discoloration of clothes due to the precipitated soap.

V. CALCULATION

VI. ANSWERS TO QUESTIONS 1. Explain the difference in in the solubility of benzoic acid and sodium benzoate in water. Which of the two would you predict to be more soluble in CHCl 3? Explain. The different behavior towards nucleophiles of carboxylic acids derivatives is a consequence of structure. In the case of benzoic acid, the C=O carbon is electron rich making the compound less ready to react with water, a nucleophile. The more electron-poor  the C=O carbon, the more readily the compound reacts with nucleophiles. When placed in water, sodium benzoate dissociates to form sodium ions and benzoic acid ions. It is a weak organic acid that contains a carboxyl group. This accounts for the higher solubility of sodium benzoate in water. 2. Based on the results in Part A.2, what can be said about the relative acidities of  phenols and carboxylic acids? Arrange the following compound types in order of  increasing acidity: carboxylic acid, alcohol, phenol and water. Carboxylic acids are much more acidic than alcohols even though both contain O²H group due to the relative stabilities of carboxylate anions versus alkoxide anions. In an alkoxide ion, the negative charge is localized on one oxygen atom. In carboxylate ion, however, the negative charge is delocalized, or spread out over both oxygen atoms. In other  words, a carboxylate ion is a stabilized resonance hybrid of two equivalent structures. Phenols, on the other hand, are more acidic than alcohols because the phenoxide anion is resonance-stabilized by the aromatic ring. Sharing the negative charge over the ring increases the stability of the phenoxide anion and thus increases the tendency of the corresponding phenol to dissociate. Therefore, carboxylic acids > phenols > alcohols in terms of their acidities. 3. Based on the results in Part B, arrange the following compound types in the order of  decreasing hydrolysis rate: acid halides, acid anhydrides, esters, and amides. Give the theoretical explanations for the observed differences in reaction rates. The more highly polar a compound is, the more reactive it is. As confirmed by the results of the experiment, the polar acid halides are the most reactive of the carboxylic acid derivatives because the electronegative halide atom strongly polarizes the carbonyl group. Acid anhydrides react in almost the same manner as acid halides, although at a slower rate. Only ³half´ of the anhydride molecule is used. The other half acts as the leaving group during the nucleophilic acyl substitution step and produces carboxylate anion as a byproduct. Thus, anhydrides are inefficient to use, and acid chlorides are normally preferred for introducing acyl substituents other than acetyl groups. Esters show the same kinds of  chemistry as the first two compounds mentioned, but are less reactive toward nucleophiles than acid chlorides or anhydrides. The slowest to hydrolyze are the amides since their  linkage is very stable and is enough to serve as the basic unit from which proteins are made.

4. The soap water water mixture a true solution? Cite examples to support your answer. A soap solution is not a real solution but a colloidal mixture that aroused after the addition of soap to water. It is considered a colloid, a cloudy mixture where one substance is dispersed evenly throughout another. Because of this effective dispersal, some colloids have are mistaken to be solutions since they have similar appearances. 5. What is a colloidal mixture? mixture? How does a colloidal mixture arise when when soap is mixed with water? A colloid or colloidal dispersion is a substance with components of one or two phases. It is a heterogeneous mixture where very small particles of one substance are distributed evenly throughout another substance. A colloidal mixture has an outer layer of  ions with the same charge so that these repel each other. This results to lesser aggregation to form particles that are large enough to precipitate. Oil is a pure hydrocarbon so it is non-polar. The non-polar hydrocarbon tail of the soap dissolves into the oil. That leaves the polar carboxylate ion of the soap molecules sticking out of the oil droplets. These spherical clusters, called micelles, which surfaces are negatively charged is where droplets of grease or oil are solubilized in water. Then, they become coated by the hydrophobic non-polar tails of soap molecules. As a result, the oil droplets repel each other and remain suspended in solution to be washed away by a stream of water. 6. On the basis of the litmus litmus test, are the soap-water and detergent-water mixtures acidic, basic or neutral? Explain the difference, if any in the reactions of the soapwater and detergent-water mixtures to litmus paper. Reaction with litmus paper shows the alkalinity of both soap-water and detergentwater mixtures. Soaps undergo a hydrolysis reaction upon hydration and as a result, they tend to be alkaline. Detergent-water mixtures are also alkaline but in a lesser degree. 7. Which would you you predict to have a greater emulsifying emulsifying power in ³hard water´, soaps or synthetic detergent? Explain. Synthetic detergents have greater emulsifying in ³hard water´ because of the presence of the sulfonate group in detergents. The sulfonate group doesn¶t react with the calcium and magnesium ions in hard water to form films or scums, a property typical of  soaps. 8. Explain the cleaning property of soaps soaps and detergents based on your observations of  their emulsifying action. The cleaning action of both soaps and detergents results from their ability to emulsify or disperse water-insoluble materials (dirt, oil, grease, etc.) and hold them in suspension in water. This ability comes from the molecular structure of soaps and detergents. When a soap or detergent is added to water that contains oil or other water-insoluble materials, the soap or detergent molecules surround the oil droplets. The oil or grease is ³dissolved´ in the alkyl groups of the soap molecules while the ionic end allows the micelle to dissolve in water. As a result, the oil droplets are dispersed throughout the water, as emulsification takes place, and can be rinsed away.