Essentials of Fragrance Chemistry

By Matthew Tittensor, Nicholas Lang, and Sohum Sanghvi

Two more common hygiene products are perfume and cologne.  We know that these sprays smell nice and permeate throughout a room, but what is it that gives them their scent and more importantly why does it disperse?  In today’s blog post we will get into this by discussing the organic structures of esters, specific scents, commercial uses for esters, and the process of diffusion.

           An ester follows the format follows the format of the image to the right, with the R group being any hydrocarbon.  This is written a RCO2R’.  The alcohol component makes up the basis of the alkyl component and R’OH’s root name and is based on the longest chain with an OH attached to it. Meanwhile, RCO2H is the carboxylic acid, from which the –oate in the name is derived from.  The full name for an ester is an alkyl alkanoate. Now that the nomenclature is out of the way, what do esters smell like and would they be used in perfumes?

Esters often have a pleasant fruity aroma as can be seen in the chart to the right.  However, that does not necessarily make them ideal for perfumes.  Most simple esters give off these pleasant smells, but problems arise because they are not prepared to handle the sweat that a human body releases.  This sweat hydrolyzes the simple ester and can replace this seemingly nice smell with a harsh one.  A common example is that butyric acid smells like rancid butter, but ethyl butyrate, an ester it can be derived from, smells like pineapples.  This is one reason that simple esters are not utilized in the perfume industry.  However, perfumeries get around this by often including many esters in their products as well as essential oils to prevent the hydrolysis of the esters.  Esters serve a role in the food and beverage industry as well.

           Would you rather eat a delicious food that smells rancid or a mediocre food that smells delicious, if you did not know how each one tasted?  This is a problem that major manufacturers come to face when they make their products.  These companies utilize a combination of esters and essential oils as well to produce a scent that is please to both smell and taste.  It is not so simple as getting one pleasant odor and taste either, as the human has over 9000 taste receptors on its tongue and smell plays a large role in perception of taste.  To create an ideal, it takes a lot of testing and a wide variety of organic and synthesized compounds to be used.

           Diffusion is the movement of molecules from an area that contains a higher concentration to one with a lower concentration of the molecule.  These molecules are already in constant motion and move in random directions due to the random collisions that they experience with each other and other particles.  The net movement is always towards the lower concentrated expanse as more collisions occur on a more highly concentrated zone, making it more likely for the molecule to be pushed over to the other area.  Dynamic Equilibrium only comes to exist after the concentration gradient, difference in molecule distribution, is removed.  This applies to perfumes and colognes as they emanate from their more highly concentrated location on the wrist or neck to the areas surrounding the wearer.  This creates a nice scent around the user and fulfills the purpose of removing or covering up body odors.

We have taken a look at the concept of esters, specific scents, commercial uses for esters, and basics about the process of diffusion. Using the right ester is vital for obtaining the scent that is wanted, and diffusion is important for making sure the scent remains on the user and covers the body odors. In our next blog post, we will continue our discussion on fragrances and continue to unveil interesting chemistry behind perfumes and colognes.

Breaking Down the Chemistry of Soap

Created by Matthew Tittensor, Nicholas Lang, and Sohum Sanghvi

Introduction

We have examined many aspects of soap and shampoo thus far; Creation, Chemical Composition, interaction with water, and even why soap bubbles. This section will take a closer look into some chemistry aspects involved with soap, as well as as the creation and mass production of soap products on a small and large scale.

A Closer Look at the Soap-Making Process

In our previous blog post, we discussed some basic properties of how soap is made using the saponification reaction. With the help of La Shonda Tyree, owner of Handmade Soap Coach, we were able to understand various thermodynamic and kinetic properties of this reaction.

Thermodynamics

The first part of the saponification reaction is ionization, which takes place when sodium hydroxide is mixed with water. This ionizes, or breaks down the sodium hydroxide into separate sodium ions and hydroxide ions. When this happens, the water temperature increases to as much as 200°, and thus the reaction is exothermic to get rid of this excess heat. Dissolution of NaOH Demo

In the previous blog post, we discussed the formation of triglyceride molecules from fatty acids and glycerol. For the next step of saponification, the triglyceride needs to be broken down into fatty acids and glycerol through a two step process called steam hydrolysis. The steam hydrolysis yields a fatty acid without its salt as well as glycerol. Then, the sodium ions (from the ionization) hook up with the fatty acids to form a fatty acid salt, or a sodium soap. The hydroxide ions attach to the glycerol to form glycerin. Note that because of the high-temperature steam hydrolysis, the overall enthalpy of the saponification reaction isendothermic.Saponification Reaction
The fat/oil can be considered as the triglyceride being treated by the Na+ and OH- ions. Note that heat is required for the reaction to be completed. 

Temperature is an important aspect of the reaction. When combining the triglyceride and sodium hydroxide solution, having a temperature of less than 120° is ideal, since a higher temperature will speed up the reaction too much. The addition of scent ingredients, such as honey, milk, cinnamon, and clove can affect the reaction’s heat by increasing the temperature of the raw soap. These ingredients should be handled properly, since having too many ingredients will cause the heat to increase too much and cause the soap to separate during the hottest phase of saponification (called the gel phase) during which the soap is in a mold. If the ingredients are properly added to the soap, the soap will harden without falling apart in the cooling and hardening phase.

Kinetics:

As mentioned before, the use of heat definitely impacts the rate of the saponification reaction. If the reaction takes place at a temperature higher than 120°, the raw soap will saponify too quickly and become thick. Additionally, the crafter would not have enough time add scent, color, and herbs to the raw soap. Having a thick raw soap may make it difficult to pour into molds.

The reaction rates for saponification are based on the method that is used to create the soap. The two common methods for producing soap are the cold process and the hot process. The cold process for making soap takes 18 to 24 hours to complete the saponification process. The hot process requires only two hours for the saponification reaction because it is reheated by a double boiler. The soap from the cold process requires at least 2 weeks to “cure” in which the soap loses water to eventually become hard. The hot process usually requires only one week to harden. Cold process soap tends to be of higher quality, and the remaining glycerin from the saponification reaction is usually added to the soap as a natural skin softener. The cold process soap also tends to have more designs since it is not heated in extremely high temperatures.

The Difference Between Liquid and Solid Soap:

While soaps come in many varieties, the most easily distinguishable types are hard and soft soaps.  Soap is made during the process in which a base reacts with a fat, either a vegetable oil or an animal fat.  This base ultimately determines the final state of the soap.  A sodium hydroxide base results in a harder soap unlike the soap produced by potassium hydroxide. Another factor is what kind of fat is used.  A soft oil will make liquid soap easier to form more purely and with a more clear complexion.   The difference of physical states between the two caustic bases is practical because it allows for different functions.  For instance KOH is used often in making shaving cream as it is very soluble in water.  Other reasons for having both varieties of soap include catering to a wider market of people; many people have a distinct preference in soap and having variety allows for many people to be reached.  makes a liquid soap as opposed to 

Mass Production of Soap:

    In large amounts, soap is created in factories for commercial purposes, but through a variety of different ways. One such fashion, as described by the Alabu Soap Company, begins with over an ounce of goat milk, coconut oil, food-grade oils, and soybean oil. After the oils are melted, olive oil is added. In some specific soaps, exotic oils are added as well, such as Squalane and Shea Butter. The mixture is mixed with lye and poured into molds, to set for 12 hours. After this period, it is put through a conveyor belt with high-tension strings on the end to be cut into individual bars, as the mold created a solid about 5 feet long. After 4 weeks, the soap is ready to be packaged and sent away.

Another way of creating soaps is called the hot process.In contrast to cold processes of making soap, hot processed soap saponifies during or immediately after the mixture is handled by people/machines, whereas the cold process takes a while longer to saponify. In hot processes, the hydroxide and lipids are mixed just below the boiling point of the solution, allowing them to saponify faster. The advantage of doing so is that one does not need to know the exact amount of Hydroxide in the mixture.

Performing the cold processing method of soap-making requires more careful consideration and planning. The exact amount of oils and fats must be known. Also, the saponification values of the oils and fats must be consulted in the corresponding saponification chart. Too much lye, for instance, can make soap irritable to the skin.

During this process, lye is dissolved in water, and the oils are made into a warm liquid state,either by heating a liquid or melting a solid. They are mixed until two stages are fully emulsified.

Bonus Video: The How It’s Made series has a video on the production of soap bars. This further explains the commercial production of soap.

We would like to give special thanks to Ms. La Shonda Tyree of Soap Coach for her input for our blog post.

Fragrance Chemistry: Another Look

In our previous blog post, we introduced concepts from organic chemistry, such as esters, commercial uses of esters, and the process of diffusion. Before we continue in our discussion about esters and fragrances, it is probably important to learn about how smell actually occurs.

How Smell Occurs (the Chem Way!)

Everything that we smell, whether it is food, smoke, wood, soap or shampoo, emits molecules that reach our nose. The molecules that are emitted are all volatile and relatively light. As we have learned, to be a volatile substance, it must be easily to evaporate. Objects that have no smell, such as NaCl, behave this way because they are non-volatile solids.

Behind the inside of one’s nose lie a set of neurons. Unlike many other sets of neurons in our body, they are regularly exposed to oxygen. Also, these neurons have cilia, or tiny hairs, that are special to the nose. the molecule emitted from our volatile substance  attach to the cilia in our nostrils and trigger a sensation in the neurons of our nose. The neurons send a signal to our brain that translates it into a smell.

But, the inquisitive mind may ask, what molecules are emitted from our volatile objects that enter our nostrils? Many natural objects and plants emit molecules that are present when the object undergoes esterification. A banana, for instance, emits the ester isoamyl acetate (CH3COOC5H11.) Oranges produce Octyl Acetate (CH3COOC8H17) when they undergo the same process.

 

How Perfume Works

As you may or may not be aware, perfume is very dilute. Someone may think it is because the producer’s of the perfume are trying to minimize their costs, possibly to the detriment of the product, but this is not the case. In mixtures such as perfume, there are a variety of different alcohols in the same liquid. Alcohols all are very strong-scented; they emit many molecules that are received by the cilia in your nostrils. If it were a very concentrated substance, perfume would give off all the smells of the different alcohols within it simultaneously. Although they might be sweet on their own, the smells together would not be nearly as enjoyable, as we can no longer distinguish one from the other.

Perfumes contain different alcohols mostly due to the way they are supposed to work. There are three stages to perfume smells; top notes, heart notes, and base notes. Top note smells occur within 15 minutes of spraying the perfume on your skin. These chemicals are the first to evaporate, and thus the first molecules to be received by your nostrils. These scents are strange or exotic, and are made that way to interest consumers, yet not stay too long to be sick of them. Heart note smells occur 3-4 hours after application. These are generally the floral smells of a perfume. Base note smells occur 5-8 hours after application, and are usually musky or mossy. The relation to kinetics is the rate it takes for each individual scent to be activated. This can be represented using rate laws and reaction coordinate diagrams, to indicate exactly which scents are being activated at what time. The rate for the top notes will be the fastest, followed by the heart notes and base notes.

One must be careful with perfume, as light has enough energy to speed the decay of top note chemicals. Air also corrodes the fragrance through oxidation, and this occurs quicker after application. Also, top notes will evaporate faster on warmer skin that is less oily than on cold and oily skin. It is because of this that one must store their perfume in a dark, room temperature area to maximize its shelf life.

Classifying Perfumes

In the previous section, we mentioned how the duration of perfumes can help in classifying a perfume. Another way for classifying perfumes is by their smell. As we know, esters give the perfume its fragrance. A consultant in the fragrance industry, Michael Edwards, devised a qualitative way of describing fragrances for perfumes. This classification can be seen in the fragrance wheel, as shown in the picture below.

We know that perfumes can have scents, and that esters have the ability to cover up scents. But, how do we actually create a perfume? That question will be answered in the next section.

 How Perfumes Are Made

First, all ingredients necessary for a perfume must be obtained. A perfume can have over 100 different ingredients, so this step is essential. This process may of extracting oils from plants, extracting scents from fatty substances of animals, or using synthetic fragrances developed by chemists. For example, the citrus tree blossom or the myrrh resins can be extracted and used in perfumes.

 

These ingredients are grouped into 4 categories: primary scents, modifiers, blenders, and fixatives. The primary scents are the most important scents required to give a perfume its scent. The modifiers are often esters, such as having a fruity ester and floral ester to make the scent fruity floral. Modifiers essentially replace one scent with one more geared towards the perfume scent, just like how an ester replaces an odor. The blenders and fixatives add some more scent to the primary scent to make it easier to transition between the three stages (top, heart, and base notes).

After all the scents are gathered, the scents are blended together to create the perfume. After the blending of ingredients, ethyl alcohol and water is added. The amount of alcohol added is based on what strength of the perfume is desired. The concentration of the perfume mixture is often mentioned in units of either volume percent or weight/volume percent. The perfume is then aged in tanks for several weeks and filtered before being put into bottles.

The fragrance industry is a large, growing industry in the world, and new formulas are constantly being developed for new fragrances. It is important to remember that alcohol is added to fragrances to give them scents that come in three notes or phases, the top note, heart note, and base note. Fragrances can be grouped by their qualitative scents by the fragrance wheel as well as by their duration. The process of making fragrances can involve many ingredients of various types, and can be altered to create new fragrances for commercial sale.

We hope you enjoyed reading our series of blog posts! Thank you for your support!

Shampoo Chemistry

Do you use shampoo?  Right now, you’re probably thinking, “That’s a silly question, of course I use shampoo.  How else would I keep my hair clean and luscious?”  However, I bet that you don’t know too much about what is in your shampoo or why it cleans your hair.  Why would you; it’s not as if you’re lathering a diverse group of chemicals into your head, right? If you read on, you will become educated about what is in a shampoo and how it works.

Shampoo Basics

Let’s start with the basics, what does shampoo do to your hair?  Intuitively, one would say that shampoo is used to clean hair. Hair must be kept clean to prevent hair from becoming oily and greasy by a substance called sebum. Sebum keeps your hair healthy and protected, but also attracts dirt, causing hair to become greasy. Shampoo contains sulfates that, when rinsed with water, carry oily substances out of your hair. Thus, shampoo actually cleanses and dries hair. Moisturizers can be added to shampoos to allow the hair to retain water, and become moisturized. Conditioners can also be added to prevent tangling of hair. There can be other additives to shampoo, such as UV-absorbers and colorants, but ultimately, the purpose of shampoo is to successfully clean and dry hair.

Click the picture for a more detailed view from Chemistry Views.

Shampoo Components and Applications           

Shampoo has many components and each has a specific role. Major components, aside from water, are surfactants, conditioning agents, and preservatives.  Shampoo manufacturers look at aesthetic qualities, foaming agents, pH buffers, and thickeners.  The surfactants clean your hair.  These molecules are both hydrophobic and hydrophilic. The hydrophobic tail consists of hydrocarbons with a chain length of between C8 and C18.  The shorter the chain is, the greater power to remove grease it will have. However these chains are harsh on hair.  A long chain is very mild, but does a lot less to clean hair, so most manufacturers will use a chain of roughly length C12.  The hydrophilic head is made of many functional groups and the surfactant’s nature will likely be determined by this part of the molecule.  The four types of surfactants are anionic, cationic, nonionic, and amphoteric. Anionics will foam and clean your hair more than the other types of surfactants. The most common forms are sodium laureth sulfate, sodium lauryl sulfate, and ammonium lauryl ether sulfate.  The ammonium group has the properties of an increase in steric hindrance and a low ionization level, so it is most commonly used in a bottle of 2 in 1 shampoo and conditioner. This is because the cationic surfactants are used as conditioners, and can cause both the anionics and the cationics to precipitate out, but the properties of the ammonium group prevent this.  Cationics cling to the hair and do not come off easily, which leaves the hair shiny.  The most commonly used cationic surfactant is polyquarternium-10 which is a cellulosic polymer that is quarternised for ideal results.  Nonionics are very uncommon today and probably do not apply to your shampoo unless it specifically targets grease build up. This is because a nonionic surfactant is very damaging to the hair.  It strips away all of the fats and can leave the hair damaged and irritating. Amphoteric surfactants are just the opposite.  They are present in most shampoo because they are extremely mild and produce an excellent lather.  These surfactants carry both a positive and a negative charge unlike nonionics which do not carry a charge and the most commonly used one is cocamido propyl betaine.  To condition your hair, a glycerol or a silicone polymer is added.  These add shine, but accumulate on hair.  Some other aspects of conditioners are that they make hair easy to comb with cetyl alcohol and shiny with cetrimonium bromide.  If you are looking to buy an individual conditioner, polyquats or PEG fatty glycerides are used, as they work better and are easier to remove.  There are innumerable preservatives and there will be at least four in your shampoo as a wide range may be necessary to kill all potential microbes.  In an aesthetic sense, there are many fragrances for scent, opacifiers and colorants for the appearance of the shampoo, and UV-absorbers to protect the shampoo from the Sun. Foaming agents do not help to clean, but they do aid in producing a better lather.  pH buffers are used to keep the shampoo acidic.  At a pH level of five the hair is shiny and sleek, but at higher pHs of seven to nine, the hair becomes dull.  Thickeners are for convenience as they prevent the shampoo from running freely as it leaves the bottle as well as to make the shampoo viscous enough that it does not run into your eyes.

 

Relations to Properties of Solutions

To show the entire chemistry behind shampoo, let us assume that it contains conditioners and surfactants. The surfactants are anionic, or negatively charged, and conditioner molecules are cationic, or positively charged. To prevent the two from coming together and depositing out of solution, the conditioner molecules form a crystalline matrix around themselves. At high concentration, the surfactant molecules are stable with the conditioner matrix. Before washing the hair, the sebum gland protects the hair from drying out, but attracts dirt and is not water soluble. Once shampoo is applied, the surfactants form a colloid, or are in suspension, around the dirt and grease molecules. Then, the surfactants carry the dirt and grease molecules out of the hair. The hydrophobic end of the surfactants attaches itself with these molecules, and the hydrophilic end allows these molecules to be washed away by water. After the hair is rinsed with water, the surfactant concentration is diluted, causing the conditioner matrix to lose its stability and release conditioner molecules. Since the surface of the hair has been negatively charged by the surfactants, the cationic conditioner molecules are attracted to the hair, and provide a coating. This smooths out any roughness caused by surfactant molecules.