SCHIFF BASES
Definition of SCHIFF‘S BASE
A Schiff base (named after Hugo Schiff) is a compound with the general structure R1R2C=NR' (R' ≠ H).
They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure — Schiff, Ugo (1866)
An organic compound formed by a reaction between an aldehyde or ketone with a primary amine, e.g. hydroxycitronellal forms a Schiff s base with methyl anthranilate to give Aurantiol® — David Pybus and Charles Sell
Easier way:
Schiff base is a compound formed from the condensation reaction between an aldehyde and primary amine and produces water as a byproduct. Amines commonly employed in the fragrance industry are methyl anthranilate and ethyl anthranilate, whereas aldehyde compounds commonly used in the fragrance are alkyl or aldehyde aromatics, terpene aldehydes, such as hydroxycitronellal — Irawan, Candra & Indryati, Suci & Lestari
Why are Schiff bases IMPORTANT?
Schiff bases are so important from the fact that they increase both the chemical stability and tenacity of the aldehyde component. The father of these compounds is Hugo Schiff: Ugo (Hugo) Joseph Schiff, one of the founding fathers of modern chemistry.
The Schiff’s bases are less reactive than the free aldehyde and, since the molecular weight is much higher, they are less volatile. Thus, loss of the aldehyde by both chemical reaction and evaporation is slowed down. Moreover, hydrolysis of the Schiff’s base releases both the aldehyde and the methyl anthranilate, both of which have intense odors. Thus, use of a Schiff’s base generates a long-lived fragrance composition of the two ingredients.
Originally, the aldehydes used in these Schiff’s bases also had sweet, floral odours and so an harmonious accord was produced. Giorgio (Methyl Anthranilate + Helional) is an example of a fragrance which relies heavily on this type of accord.
The pale yellow colour of methyl anthranilate is darkened when a Schiff’s base is formed from it, because of the hypsochromic shift in the ultraviolet absorbtion maximum that results from the extension of conjugation. This colour has an effect on the colour of any fragrance in which it is incorporated and has to be taken into account if colour might be deleterious in the final product — (The Chemistry of Fragrances, David Pybus and Charles Sell; Quest International, Ashford,Kent, UK)
But why do I tell you this? The answer is very simple. The perfumer can create his own reaction to make, and extend the longevity (through mw increase) of the targeted material. It’s not a little thing.
Perfume can’t be done properly if we don’t understand ingredients. That’s also my mission
Hugo Schiff
First studies
He studied chemistry and physics in Frankfurt with Böetteger and Löwe [Schiff Collection], then continued his studies in Göttingen, where he graduated in 1857 as a student of Wölher [Betti], in a climate of great scientific and cultural renewal. Friedrich Wölher, in fact, a student of Berzelius in Stockholm, following the path opened by the teacher, had been the first to synthesize from inorganic matter an organic molecule, urea; in this way, he had refuted the theory of "vis vitalis" (the presumed "vital force" inherent in organic matter) demonstrating that between organic and inorganic compounds there was no difference of metaphysical order since one was transformable into the other [Manzelli, Costa, Fontani 1999]. Thus organic chemistry was born and the way was opened to a new type of scientific research.
Karlsruhe and the escape from Germany
Ugo Schiff participated at a very young age at the Karlshrue congress where he was able to listen to Cannizzaro's thesis and where Mendeleev [McPherson] was also present. Expatriated from Germany since 1856 (he came back to Göttingen only for the degree) [Guareschi], after a stay in Bern, where he was Free Lecturer [Pellizzari] and Charged in the University, from 1862 he moved to Italy, following his elder brother Moritz [Betti], physiologist and among the first disseminators, in Germany, of Darwin's ideas.
The reasons for this estrangement from Germany are attributable both to the Jewish origins of the family and to the socialist political ideas of the two brothers [Guareschi]; it is said in fact that Ugo, who had participated together with his brother Maurizio (older than ten years) in the insurrectional uprisings of 1848, was a friend and correspondent of Karl Marx [Pellizzari] [Poggi].
Schiff arrives in Florence
In Italy Schiff was initially "help" for two years teaching chemistry at the University of Pisa until in 1864 the Minister of Education Carlo Matteucci called him to hold the first chair of Chemistry in Florence [Betti]. In fact, at the Royal Museum of Florence, a chemistry course had been formally established in 1807, but in reality, after the resignation in 1808 of Giuseppe Gazzeri due to the inadequacy of the premises chosen, the teaching of the discipline had never been started [Gelsomini 1988]. Schiff was, therefore, to all intents and purposes, the first professor of chemistry at the Royal Institute of Advanced Practical Studies of Florence, the future University.
Researches
Except for two years spent in Turin (1877-79) where he held the positions of Professor of General Chemistry and Director of the Pharmaceutical Laboratory [Betti], Schiff remained in Florence for his entire career, fifty years long: from 1864 until his death in 1915. His research focused on organic and inorganic chemistry, physical chemistry, analytical chemistry, mineralogical chemistry, and the chemistry of natural substances [Guareschi]. Important his studies on boric ethers, on glucosides and arbutin, on tannin and gallic acid, on aromatic oxoacids and asparagine, on urea derivatives [Rolla]. He also developed the analysis then applied by Sörensen for the dosage of amino acids in urine [Rolla]. Another important discovery was thionyl chloride.
The schiff bases
Schiff's name is known throughout the world for the bases that bear his name, the "Schiff bases," and for the Fucsinic or "Schiff reagent”.
Schiff bases, products of the reaction between aromatic amines and aromatic aldehydes, still have important applications today, both in the synthetic field and in medical and biological fields (they are used for example in the determination of transaminases).
Schiff's reagent is used all over the world in the histological field for the PAS Reaction (Periodic Acid-Schiff) in which tissue pathologies are detected thanks to a histochemical reaction that leads to the formation of an intensely colored leukobase of Schiff.
It is also used, among other things, to determine the sequence of DNA fragments.
The nitrogen meter
His proverbial parsimony, based on three "principles": Everything that is not a precision instrument can be improvised - You don't have to buy what you can do yourself - You have to recover what you can still use - led him to build on his own, often improving them, many apparatus and laboratory instruments [Grassini]. Among these, the most important and innovative is the azotometer, which also bears his name: Schiff's azotometer.
La Gazzetta Chimica Italiana
During his career, Ugo Schiff wrote about four hundred scientific articles in prestigious Italian and international journals, such as "Liebig Annalen der Chemie" and "Berichte der Deutschen Chemischen Gesellschaft". He also published three books, including a chemistry manual. In 1870 he was among the founding members of the Gazzetta Chimica Italiana; on the first page of the magazine, kept at the Library of Science of the University of Florence, there is a holographic text of his with the list of subscribers, Schiff was also secretary of the meeting [Fiorentini, Parrini].
The honors
He had honorary degrees from various Italian and foreign Universities and was a member of many prestigious National and International Academies and Scientific Societies. In 1871 he was appointed Knight of the Crown of Italy. At his death, on September 8, 1915, the Nation of Florence dedicated the entire third page to him. The annals of the University noted: "today Ugo Schiff, the dean of our professors, is missing" [Schiff Collection].
Schiff: a founding father
Schiff in Florence was an initiator, as was Cannizzaro in Palermo in the same years and as would have been Ciamician in Bologna. Not only in Florence, but throughout Italy, he was an indispensable reference point for an entire generation of scholars [Betti]. He was a correspondent and friend of many important European chemists, including Friedrich Konrad Beilstein, Heinrich Limpricht, William Köerner, Georg Lunge, Hans Landolt, and Emil Fischer [Schiff Collection].
The roots of chemistry and new institutes
Cultured, well beyond the boundaries of his discipline, Schiff knew Italian, German and French, Hebrew, Greek, and Latin [Betti]. Although his primary interest was scientific research and chemistry in all its applications, so much so that he continued his teaching activity until he was eighty, he also devoted himself to humanistic aspects related to his discipline. He dealt with the history of chemistry, the teaching of scientific subjects, and the reorganization of university teaching. He was interested in the history of the Royal Florentine Museum, whose origins he reconstructed. Throughout his life, he worked for the Institute of Higher Studies to become a University [Betti]. He searched for more suitable spaces for teaching chemistry and for laboratories and, after having identified them in the "Palazzina dei Servi" in Via Gino Capponi, he personally took care of the architectural transformation and the setting [Schiff Collection]. In this way, he was able to organize one of the most modern and functional institutes of the time, like the largest European universities [Betti].
Civil and social commitment
Active in the cultural and civil life of the city, he was one of the founding members of the socialist newspaper "Avanti!". [Forward, 1915]. Faithful until the end of his ideas of social equality and solidarity, he devoted his entire patrimony to the establishment of a foundation to distribute subsidies to Florentine workers who had become unable to work as a result of accidents or illness [Schiff Collection]. This institute, the "Ugo Schiff Foundation", operated until 1984, promoting the reintegration into the productive fabric of tens of thousands of people in marginalized conditions or with physical or mental disabilities [Colli 2011]. Schiff also established a degree award in his name for the best experimental thesis in pure chemistry. The degree award was presented annually until 1952 [Schiff Collection].
Students and successors
Although in Italy, since the post-war period, the memory of this great character has partially fallen into oblivion, perhaps because of his German origins or socialist ideas [Tidwell], Ugo Schiff, German but Florentine by adoption, was the founder of the Florentine chemical school and one of the most important chemists at the turn of the 19th and 20th centuries. Under his guidance and supervision, handed down as particularly strict and intransigent [Betti], many of the major Italian chemists of the early twentieth century studied and worked: his successor Angelo Angeli (nominated nine times for the Nobel Prize in Chemistry), his assistant Pietro Biginelli (discoverer of Biginelli's reaction), Mario Betti (professor at the University of Bologna), Icilio Guareschi (professor at the University of Siena and then Turin), Luigi Balbiano (professor of pharmaceutical chemistry in Rome), Arnaldo Piutti (professor in Sassari and Naples and founder of the Istituto Farmaceutico di Napoli), Pietro Saccardi (Professor of Chemistry and Pharmacy and then rector of the University of Camerino), Guido Pellizzari (professor at the University of Genoa and Florence), Guido Cusmano (professor at the University of Sassari and Pisa), Adrian Ostrogovich (Professor of Chemistry in Bucharest and Cluj Napoca), Arrigo Mazzucchelli (Chemist at the Laboratory of the Istituto Superiore di Sanità), Ugo Monsacchi (Chemist at the Follonica Foundries), Ettore Pons (Director of the Municipal Chemical Laboratory of Florence), Guido Bargioni, etc.. . From the school of Schiff a circle of scholars of the highest level was born, who exported their teaching to the major Italian universities and the world of industry.
Schiff died on September 8, 1915. The funeral was very simple, as per his will. His remains rest at the cemetery of Trespiano, in Florence, together with those of his wife and mother.
La Collezione Schiff, conservata al Dipartimento di Chimica dell'Università di Firenze, racconta attraverso gli oggetti e gli scritti originali l' eredità chimica di questo grande personaggio.
Sources and information:
— Schiff, Ugo (1866). "Sopra una nova serie di basi organiche" [On a new series of organic bases]. Giornale di Scienze Naturali ed Economiche (in Italian). 2: 201–257.
— The Chemistry of Fragrances, David Pybus and Charles Sell; Quest International, Ashford, Kent, UK
— Irawan, Candra & Indryati, Suci & Lestari, Endang & Hidaningrum, Arinzani & Supriyono, Supriyono. (2018). Synthesis and Characterization of Aurantiol Schiff Base: Relationship Between Synthesis time and some Physical Properties. Oriental Journal of Chemistry. 34. 394-400. 10.13005/ojc/340142.