1.
Melting point
–
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
2.
Sherry
–
Sherry is a fortified wine made from white grapes that are grown near the town of Jerez de la Frontera in Andalusia, Spain. Sweet dessert wines are made from Pedro Ximenez or Moscatel grapes. The word Sherry is an anglicisation of Xeres, Sherry was previously known as sack, from the Spanish saca, meaning extraction from the solera. In 1933 the Jerez Denominación de Origen was the first Spanish denominación to be recognised in this way. Jerez-Xeres-Sherry and sharing the same governing council as D. O, after fermentation is complete, the base wines are fortified with grape spirit in order to increase their final alcohol content. Wines classified as suitable for aging as Fino and Manzanilla are fortified until they reach an alcohol content of 15.5 per cent by volume. As they age in barrel, they develop a layer of flor—a yeast-like growth that helps protect the wine from excessive oxidation and those wines that are classified to undergo aging as Oloroso are fortified to reach an alcohol content of at least 17 per cent. They do not develop flor and so oxidise slightly as they age, because the fortification takes place after fermentation, most sherries are initially dry, with any sweetness being added later. In contrast, port wine is fortified halfway through its fermentation, Sherry is regarded by many wine writers as underappreciated and a neglected wine treasure. Jerez has been a centre of viniculture since wine-making was introduced to Spain by the Phoenicians in 1100 BC, the practice was carried on by the Romans when they took control of Iberia around 200 BC. The Moors conquered the region in AD711 and introduced distillation, during the Moorish period, the town was called Sherish, from which both Sherry and Jerez are derived. Wines similar in style to Sherry have traditionally made in the city of Shiraz in mid-southern Iran. Wine production continued through five centuries of Arab Empires rule, in 1264 Alfonso X of Castile took the city. From this point on, the production of sherry and its export throughout Europe increased significantly, by the end of the 16th century, sherry had a reputation in Europe as the worlds finest wine. Christopher Columbus brought sherry on his voyage to the New World, Sherry became very popular in Great Britain, especially after Francis Drake sacked Cadiz in 1587. At that time Cadiz was one of the most important Spanish seaports, among the spoils Drake brought back after destroying the fleet were 2,900 barrels of sherry that had been waiting to be loaded aboard Spanish ships. This helped to popularize Sherry in the British Isles, because sherry was a major wine export to the United Kingdom, many English companies and styles developed. Many of the Jerez cellars were founded by British families, in 1894 the Jerez region was devastated by the insect phylloxera
3.
Boca Raton, Florida
–
Boca Raton is the southernmost city in Palm Beach County, Florida, United States, first incorporated on August 2,1924 as Bocaratone, and then incorporated as Boca Raton in 1925. The 2015 population estimated by the U. S. Census Bureau was 93,235, however, approximately 200,000 people with a Boca Raton postal address reside outside its municipal boundaries. Such areas include newer developments like West Boca Raton, as a business center, the city also experiences significant daytime population increases. It is one of the wealthiest communities in South Florida, Boca Raton is located 43 miles north of Miami and is a principal city of the Miami metropolitan area, which was home to an estimated 6,012,331 people at the 2015 census. Boca Raton is home to the campus of Florida Atlantic University and the corporate headquarters of Office Depot, ADT. It is also home to the Evert Tennis Academy, owned by tennis player Chris Evert. Town Center Mall, a shopping center in West Boca Raton, is the largest indoor mall in Palm Beach County. Another major attraction to the area is Boca Ratons downtown, known as Mizner Park, still today, Boca Raton has a strict development code for the size and types of commercial buildings, building signs, and advertisements that may be erected within the city limits. No outdoor car dealerships are allowed in the municipality, additionally, no billboards are permitted, the citys only billboard was grandfathered in during annexation. The strict development code has led to major thoroughfares without large signs or advertisements in the travelers view. The original name Boca de Ratones appeared on eighteenth-century maps associated with an inlet in the Biscayne Bay area of Miami. The word ratones appears in old Spanish maritime dictionaries referring to rugged rocks or stony ground on the bottom of some ports and coastal outlets, therefore, the abridged translation defining Boca de Ratones is a shallow inlet of sharp-pointed rocks which scrape a ships cables. Residents of the city have kept the pronunciation of Boca Raton similar to its Spanish origins, in particular, the Raton in Boca Raton is pronounced as /rəˈtoʊn/ instead of /rəˈtɑːn/. The latter is a common mispronunciation by non-natives to the region, the area today known as Boca Raton was originally occupied by the Tequesta tribe, a Native American people that occupied an area along the southeastern Atlantic coast of Florida. What Spanish voyagers called Boca de Ratones was originally located to the south, by mistake since the 19th century, mapmakers moved this location to the north and began referring to the citys lake, today known as Lake Boca Raton, as Boca Ratone Sounde. The area was largely uninhabited after the Indigenous people were cleared from the area by the Spanish and he surveyed and sold land from the canal to beyond the railroad north of what is now Palmetto Park Road. Early settlement in the area increased shortly after Henry Flaglers expansion of the Florida East Coast Railway, in the citys early history during the Florida land boom of the 1920s, several investors were interested in turning Boca Raton into a resort town. Most famously, Addison Mizner had several projects for resorts and mansions in the area and he first constructed his Administrative Buildings and a small hotel to house interested investors
4.
Distilled beverage
–
This process purifies it and removes diluting components like water, for the purpose of increasing its proportion of alcohol content. As distilled beverages contain more alcohol, they are considered harder – in North America, as examples, this term does not include beverages such as beer, wine, sake, and cider, as they are fermented but not distilled. These all have relatively low alcohol content, typically less than 15%, brandy is a spirit produced by the distillation of wine, and has an ABV of over 35%. Other examples of distilled beverages include bourbon, vodka, gin, rum, tequila, mezcal, whisky, scotch, the term spirit refers to a distilled beverage that contains no added sugar and has at least 20% alcohol by volume. Distilled beverages bottled with added sugar and added flavorings, such as Grand Marnier, Frangelico, Distilled beverages generally have an alcohol concentration higher than 30%. The origin of liquor and its close relative liquid was the Latin verb liquere, according to the Oxford English Dictionary, an early use of the word in the English language, meaning simply a liquid, can be dated to 1225. The first use the OED mentions of its meaning a liquid for drinking occurred in the 14th century and its use as a term for an intoxicating alcoholic drink appeared in the 16th century. The term spirit in reference to alcohol stems from Middle Eastern alchemy and these alchemists were more concerned with medical elixirs than with transmuting lead into gold. The vapor given off and collected during a process was called a spirit of the original material. Distilled water was described in the 2nd century AD by Alexander of Aphrodisias, the Alexandrians were using a distillation alembic or still device in the 3rd century AD. The medieval Arabs learned the process from the Alexandrians and used it extensively. Freeze distillation involves freezing the alcoholic beverage and then removing the ice, the freezing technique had limitations in geography and implementation limiting how widely this method was put to use. The earliest evidence of distillation of alcohol comes from the School of Salerno in southern Italy during the 12th century. Again, the Chinese may not have been far behind, with evidence indicating the practice of distillation began during the 12th century Jin or Southern Song dynasties. A still has been found at a site in Qinglong, Hebei. Fractional distillation was developed by Taddeo Alderotti in the 13th century, the production method was written in code, suggesting that it was being kept secret. In 1437, burned water was mentioned in the records of the County of Katzenelnbogen in Germany and it was served in a tall, narrow glass called a Goderulffe. Claims upon the origin of specific beverages are controversial, often invoking national pride, but they are plausible after the 12th century AD and these spirits would have had a much lower alcohol content than the alchemists pure distillations, and they were likely first thought of as medicinal elixirs
5.
Jmol
–
Jmol is computer software for molecular modelling chemical structures in 3-dimensions. Jmol returns a 3D representation of a molecule that may be used as a teaching tool and it is written in the programming language Java, so it can run on the operating systems Windows, macOS, Linux, and Unix, if Java is installed. It is free and open-source software released under a GNU Lesser General Public License version 2.0, a standalone application and a software development kit exist that can be integrated into other Java applications, such as Bioclipse and Taverna. A popular feature is an applet that can be integrated into web pages to display molecules in a variety of ways, for example, molecules can be displayed as ball-and-stick models, space-filling models, ribbon diagrams, etc. Jmol supports a range of chemical file formats, including Protein Data Bank, Crystallographic Information File, MDL Molfile. There is also a JavaScript-only version, JSmol, that can be used on computers with no Java, the Jmol applet, among other abilities, offers an alternative to the Chime plug-in, which is no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS9. Jmol requires Java installation and operates on a variety of platforms. For example, Jmol is fully functional in Mozilla Firefox, Internet Explorer, Opera, Google Chrome, fast and Scriptable Molecular Graphics in Web Browsers without Java3D
6.
Organic chemistry
–
Study of structure includes many physical and chemical methods to determine the chemical composition and the chemical constitution of organic compounds and materials. In the modern era, the range extends further into the table, with main group elements, including, Group 1 and 2 organometallic compounds. They either form the basis of, or are important constituents of, many products including pharmaceuticals, petrochemicals and products made from them, plastics, fuels and explosives. Before the nineteenth century, chemists generally believed that compounds obtained from living organisms were endowed with a force that distinguished them from inorganic compounds. According to the concept of vitalism, organic matter was endowed with a vital force, during the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various fats and he separated the different acids that, in combination with the alkali, produced the soap. Since these were all compounds, he demonstrated that it was possible to make a chemical change in various fats, producing new compounds. In 1828 Friedrich Wöhler produced the chemical urea, a constituent of urine, from inorganic starting materials. The event is now accepted as indeed disproving the doctrine of vitalism. In 1856 William Henry Perkin, while trying to manufacture quinine accidentally produced the organic dye now known as Perkins mauve and his discovery, made widely known through its financial success, greatly increased interest in organic chemistry. A crucial breakthrough for organic chemistry was the concept of chemical structure, ehrlich popularized the concepts of magic bullet drugs and of systematically improving drug therapies. His laboratory made decisive contributions to developing antiserum for diphtheria and standardizing therapeutic serums, early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds, the development of synthetic indigo is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the methods developed by Adolf von Baeyer. In 2002,17,000 tons of indigo were produced from petrochemicals. In the early part of the 20th Century, polymers and enzymes were shown to be large organic molecules, the multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of natural compounds increased in complexity to glucose. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones, since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B12
7.
European Chemicals Agency
–
ECHA is the driving force among regulatory authorities in implementing the EUs chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and it is located in Helsinki, Finland. The Agency, headed by Executive Director Geert Dancet, started working on 1 June 2007, the REACH Regulation requires companies to provide information on the hazards, risks and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most commonly used substances have been registered, the information is technical but gives detail on the impact of each chemical on people and the environment. This also gives European consumers the right to ask whether the goods they buy contain dangerous substances. The Classification, Labelling and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU. This worldwide system makes it easier for workers and consumers to know the effects of chemicals, companies need to notify ECHA of the classification and labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100000 substances, the information is freely available on their website. Consumers can check chemicals in the products they use, Biocidal products include, for example, insect repellents and disinfectants used in hospitals. The Biocidal Products Regulation ensures that there is information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation, the law on Prior Informed Consent sets guidelines for the export and import of hazardous chemicals. Through this mechanism, countries due to hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have effects on human health and the environment are identified as Substances of Very High Concern 1. These are mainly substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment, other substances considered as SVHCs include, for example, endocrine disrupting chemicals. Companies manufacturing or importing articles containing these substances in a concentration above 0 and they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy, once a substance has been officially identified in the EU as being of very high concern, it will be added to a list. This list is available on ECHA’s website and shows consumers and industry which chemicals are identified as SVHCs, Substances placed on the Candidate List can then move to another list
8.
Boiling point
–
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the environmental pressure. A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a boiling point than when that liquid is at atmospheric pressure. For a given pressure, different liquids boil at different temperatures, for example, water boils at 100 °C at sea level, but at 93.4 °C at 2,000 metres altitude. The normal boiling point of a liquid is the case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level,1 atmosphere. At that temperature, the pressure of the liquid becomes sufficient to overcome atmospheric pressure. The standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar, the heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation, evaporation is a surface phenomenon in which molecules located near the liquids edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, a saturated liquid contains as much thermal energy as it can without boiling. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase, the liquid can be said to be saturated with thermal energy. Any addition of energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed, similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the pressure of the liquid equals the surrounding environmental pressure. Thus, the point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, at higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, the boiling point cannot be increased beyond the critical point. Likewise, the point decreases with decreasing pressure until the triple point is reached
9.
Acetaldehyde
–
Acetaldehyde is an organic chemical compound with the formula CH3CHO, sometimes abbreviated by chemists as MeCHO. It is one of the most important aldehydes, occurring widely in nature, Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants. It is also produced by the oxidation of ethanol by the liver enzyme alcohol dehydrogenase. Pathways of exposure include air, water, land, or groundwater, as well as drink, consumption of disulfiram inhibits acetaldehyde dehydrogenase, the enzyme responsible for the metabolism of acetaldehyde, thereby causing it to build up in the body. The International Agency for Research on Cancer has listed acetaldehyde as a Group 1 carcinogen, Acetaldehyde is one of the most frequently found air toxins with cancer risk greater than one in a million. In 1835, Liebig named it aldehyde, the name was altered to acetaldehyde. In 2003, global production was about 1 million tonnes, before 1962, ethanol and acetylene were the major sources of acetaldehyde. Since then, ethylene is the dominant feedstock, smaller quantities can be prepared by the partial oxidation of ethanol in an exothermic reaction. This process typically is conducted over a silver catalyst at about 500–650 °C, cH3CH2OH + 1⁄2 O2 → CH3CHO + H2O This method is one of the oldest routes for the industrial of preparation of acetaldehyde. Prior to the Wacker process and the availability of cheap ethylene and this reaction is catalyzed by mercury salts, C2H2 + Hg2+ + H2O → CH3CHO + Hg The mechanism involves the intermediacy of vinyl alcohol, which tautomerizes to acetaldehyde. The reaction is conducted at 90–95 °C, and the acetaldehyde formed is separated from water and mercury, in the wet oxidation process, iron sulfate is used to reoxidize the mercury back to the mercury salt. The resulting Iron sulfate is oxidized in a reactor with nitric acid. The process was once attractive because of the value of the hydrogen coproduct, the hydroformylation of methanol with catalysts like cobalt, nickel, or iron salts also produces acetaldehyde, although this process is of no industrial importance. Similarly noncompetitive, acetaldehyde arises from synthesis gas with modest selectivity, at room temperature, acetaldehyde is more stable than vinyl alcohol by 42.7 kJ/mol, Overall the keto-enol tautomerization occurs slowly but is catalyzed by acids. Photo-induced keto-enol tautomerization is viable under atmospheric or stratospheric conditions and this photo-tautomerization is relevant to the earths atmosphere, because vinyl alcohol is thought to be a precursor to carboxylic acids in the atmosphere. Acetaldehyde is an electrophile in organic synthesis. In condensation reactions, acetaldehyde is prochiral and it is used primarily as a source of the CH3C+H synthon in aldol and related condensation reactions. Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives, in one of the more spectacular condensation reactions, three equivalents of formaldehyde add to MeCHO to give pentaerythritol, C4
10.
Density
–
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
11.
Simplified molecular-input line-entry system
–
The simplified molecular-input line-entry system is a specification in form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules, the original SMILES specification was initiated in the 1980s. It has since modified and extended. In 2007, a standard called OpenSMILES was developed in the open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. The Environmental Protection Agency funded the project to develop SMILES. It has since modified and extended by others, most notably by Daylight Chemical Information Systems. In 2007, a standard called OpenSMILES was developed by the Blue Obelisk open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, in July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is generally considered to have the advantage of being slightly more human-readable than InChI, the term SMILES refers to a line notation for encoding molecular structures and specific instances should strictly be called SMILES strings. However, the term SMILES is also used to refer to both a single SMILES string and a number of SMILES strings, the exact meaning is usually apparent from the context. The terms canonical and isomeric can lead to confusion when applied to SMILES. The terms describe different attributes of SMILES strings and are not mutually exclusive, typically, a number of equally valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol, algorithms have been developed to generate the same SMILES string for a given molecule, of the many possible strings, these algorithms choose only one of them. This SMILES is unique for each structure, although dependent on the algorithm used to generate it. These algorithms first convert the SMILES to a representation of the molecular structure. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database, there is currently no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, and these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES
12.
Acetal
–
An acetal is a functional group with the following connectivity R2C2, where both R groups are organic fragments. The central carbon atom has four bonds to it, and is saturated and has tetrahedral geometry. The two RO groups may be equivalent to other or not. The two R groups can be equivalent to other or not, and one or both can even be hydrogen atoms rather than organic fragments. Acetals are formed from and convertible to carbonyl compounds, the term ketal is sometimes used to identify structures associated with ketones rather than aldehydes and, historically, the term acetal was used specifically for the aldehyde cases. Formation of an acetal occurs when the group of a hemiacetal becomes protonated and is lost as water. The carbocation that is produced is then attacked by a molecule of alcohol. Loss of the proton from the attached alcohol gives the acetal, acetals are stable compared to hemiacetals but their formation is a reversible equilibrium as with esters. As a reaction to create an acetal proceeds, water must be removed from the mixture, for example, with a Dean-Stark apparatus. The formation of acetals reduces the number of molecules present and therefore is not favourable with regards to entropy. A way to improve this is to use an orthoester as a source of alcohol, aldehydes and ketones undergo a process called acetal exchange with orthoesters to give acetals. Water produced along with the product is used up in hydrolysing the orthoester. Acetals are used as protecting groups for carbonyl groups in organic synthesis because they are stable with respect to hydrolysis by bases and they can either protect the carbonyl in a molecule or a diol. That is, either the carbonyl, or the alcohols, or both could be part of the molecule whose reactivity is to be controlled, various specific carbonyl compounds have special names for their acetal forms. For example, a formed from formaldehyde is sometimes called a formal or the methylenedioxy group. The acetal formed from acetone is sometimes called an acetonide, acetalisation is the organic reaction that involves the formation of an acetal. One way of formation is the nucleophilic addition of an alcohol to a ketone or an aldehyde. Acetalisation is often used in organic synthesis to create a group because it is a reversible reaction
