The doctor sweetening process is an industrial chemical process for converting mercaptans in sour gasoline into disulfides. Sulfur compounds darken gasoline, give it an offensive odor and increase toxic sulfur dioxide engine emissions. [1] However, this process only reduces the odor.
These sulfur compounds can be removed with the following chemical reactions: [2]
The chemistry of 'doctor sweetening' was described in detail by G. Wendt and S. Diggs in 1924. They also showed that the lead oxide solution brought about oxidation of the mercaptans to the corresponding organic disulfides, which are comparatively odourless. Lead oxide (litharge) dissolves in reasonably concentrated solutions of sodium hydroxide or potassium hydroxide owing to formation of a soluble compound, sodium plumbite:
When this alkaline solution is agitated with petroleum, the two liquids do not dissolve in one another, but any mercaptan in the oil will unite with an equivalent amount of the lead (which then passes into the petroleum) to form what is called a lead mercaptide, soluble in the oil:
If the mixture is now treated with powdered sulfur, which has a high affinity for lead, a black suspension of lead sulfide forms, and conversion of the mercaptide into a so-called disulfide (which remains in the oil) is induced:
With no sulfur added, but in the presence of atmospheric oxygen, the same conversion occurs, but only slowly, and probably not completely:
It is evident that the process does not remove the sulfur from the oil but even may increase the sulfur content if too much powdered sulfur is added, and some of the lead may remain in the petroleum.
The described chemistry is also the basis of the doctor test for the sweetness or sourness of gasoline (i.e., the extent of sulfur contamination). A gasoline is described as doctor sweet if, after shaking with sodium plumbite solutions, the addition of powdered sulfur fails to produce a dark precipitate of lead sulfide.
In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water.
In chemistry, a half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of half reactions is used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery. Half reactions can be written to describe both the metal undergoing oxidation and the metal undergoing reduction.
In chemistry, a disulfide is a compound containing a R−S−S−R′ functional group or the S2−
2 anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups.
In organic chemistry, a thiol, or thiol derivative, is any organosulfur compound of the form R−SH, where R represents an alkyl or other organic substituent. The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols, and the word is a blend of "thio-" with "alcohol".
In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities are on the right-hand side with a plus sign between the entities in both the reactants and the products, and an arrow that points towards the products to show the direction of the reaction. The chemical formulas may be symbolic, structural, or intermixed. The coefficients next to the symbols and formulas of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin in 1615.
Sulfide (also sulphide in British English ) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH−) are the conjugate acids of sulfide.
Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components. It is an amphoteric oxide.
Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, therefore materials in other forms may need to be brought to this state before using standard methods. The solution is then treated with various reagents to test for reactions characteristic of certain ions, which may cause color change, precipitation and other visible changes.
A single-displacement reaction, also known as single replacement reaction or exchange reaction, is an archaic concept in chemistry. It describes the stoichiometry of some chemical reactions in which one element or ligand is replaced by atom or group.
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. The reverse of disproportionation, such as when a compound in an intermediate oxidation state is formed from precursors of lower and higher oxidation states, is called comproportionation, also known as synproportionation.
Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates, it can exist in two different forms: sodium metaperiodate (formula NaIO4) and sodium orthoperiodate (normally Na2H3IO6, but sometimes the fully reacted salt Na5IO6). Both salts are useful oxidising agents.
In organic chemistry, episulfides are a class of organic compounds that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, and thiacyclopropanes. Episulfides are less common and generally less stable than epoxides. The most common derivative is ethylene sulfide.
Lead(II) carbonate is the chemical compound with the chemical formula PbCO3. It is a white solid with several practical uses, despite its toxicity. It occurs naturally as the mineral cerussite.
Selenium compounds are compounds containing the element selenium (Se). Among these compounds, selenium has various oxidation states, the most common ones being −2, +4, and +6. Selenium compounds exist in nature in the form of various minerals, such as clausthalite, guanajuatite, tiemannite, crookesite etc., and can also coexist with sulfide minerals such as pyrite and chalcopyrite. For many mammals, selenium compounds are essential. For example, selenomethionine and selenocysteine are selenium-containing amino acids present in the human body. Selenomethionine participates in the synthesis of selenoproteins. The reduction potential and pKa (5.47) of selenocysteine are lower than those of cysteine, making some proteins have antioxidant activity. Selenium compounds have important applications in semiconductors, glass and ceramic industries, medicine, metallurgy and other fields.
Merox is an acronym for mercaptan oxidation. It is a proprietary catalytic chemical process developed by UOP used in oil refineries and natural gas processing plants to remove mercaptans from LPG, propane, butanes, light naphthas, kerosene, and jet fuel by converting them to liquid hydrocarbon disulfides.
Thiocarbonate describes a family of anions with the general chemical formula CS
3−xO2−
x (x = 0, 1, or 2):
In organosulfur chemistry, a sulfenyl chloride is a functional group with the connectivity R−S−Cl, where R is alkyl or aryl. Sulfenyl chlorides are reactive compounds that behave as sources of RS+. They are used in the formation of RS−N and RS−O bonds. According to IUPAC nomenclature they are named as alkyl thiohypochlorites, i.e. esters of thiohypochlorous acid.
