Newsgroup: it.scienza.chimica
Titolo: Cere e grassi

Come mai i grassi con NaOH si saponificano mentre
le cere no?
Grazie per l'attenzione
--
Trixt
IHGGerD #105
Tre cose solamente m'enno in grado,
le quali posso non ben ben fornire,
cioe' la donna, la taverna e 'l dado:
queste mi fanno 'l cuor lieto sentire. 

 Grazie per l'attenzione
Questione di gruppi funzionali
-- 
revenge

 mentre stavo mangiando un
petto di drago nero arrosto:

Ok, riformulo la domanda: che differenza c'e' fra
un grasso e una cera? :)
Non sono entrambi esteri di acidi grassi a catena
lunga?


 lunga?
No, la differenza con le cere consiste nel fatto che i grassi sono esteri 
del glicerolo, mentre nelle cere anche l'alcool è a catena lunga.
-- 
Ciao,
Luca
*** 
http://digilander.libero.it/luciferino_666/
 *** 

I grassi sono esteri di acidi grassi saturati con glicerina e
differiscono dagli olii per il minor numero di doppi legami. Un olio si
può trasformare in un grasso rompendo i doppi legami tra gli atomi di
carbonio e saturando con idrogeno le valenze rimaste libere (es:
margarina).
Le cere o alcoli grassi sono anch' esse costituite da acidi grassi a
lunga catena ma esterificati con alcoli. In altre parole sono  esteri
di acidi grassi con lunghe catene di alcoli. 
Ciao
Andrea Zille

Tornando alla domanda iniziale, per quanto mi ricordi io le cere
possono saponificare. Ma possono avere efficenze di idrolisi alcalina
molto basse se sono formate da lunghe catene di esteri alifatici. Tanto
che anche ci vorrebbero ore se non giorni in in NaOH o KOH per avere
una decente saponificazione.
Ciao 
Andrea Zille

Volevo essere sicuro della risposta quindi sono andato a cercare su un 
testo sacro qualcosa sulle cere ed ecco qui. Abbiamo ragione tutti
Definition
No generally accepted definition exists for the term wax. All attempts 
to formulate a precise, comprehensive, and scientifically verifiable 
definition of wax must take the large number of waxlike products and 
the chemical complexity of individual types into account. Nevertheless, 
use of the term wax for different chemical species with common 
properties is still reasonable.
Typically waxes do not consist of a single chemical compound, but are 
often very complex mixtures. Being oligomers or polymers in many cases, 
the components differ in their molar mass, molar mass distribution, or 
in the degree of side-chain branching. Functional groups (e.g., 
carboxyl, alcohol, ester, keto, and amide groups) can be detected in 
waxes, sometimes several different groups.
The academic definition still quoted in chemistry text books — that 
waxes are esters of long-chain carboxylic acids with long-chain 
alcohols — is no longer useful. It applies fairly well only to some 
classical waxes, such as beeswax; others (e.g., petroleum waxes) do not 
fall in this category. Today, physical and technical definitions are 
preferred. Several attempts were made to differentiate between waxes 
and other classes of substance, particularly fats, resins, and high 
molar mass polymers, by using several criteria. These primarily 
physical definitions are to some extent arbitrary and are not 
generalled accepted. Waxes can also be classified according to their 
applications.
Probably the most conclusive definition has been drawn up in Europe by 
the Deutsche Gesellschaft für Fettwissenschaft (DGF, German Association 
for Fat Science). It was used in modified form in the customs tariff of 
the European Union [4], [5]. According to this definition, waxes must 
have:
1)	A drop point (mp) >40 °C
2)	Their melt viscosity must not exceed 10 000 mPa · s at 10 °C above 
the drop point
3)	They should be polishable under slight pressure and have a strongly 
temperature-dependent consistency and solubility
4)	At 20 °C they must be kneadable or hard to brittle, coarse to finely 
crystalline, transparent to opaque, but not glassy, or highly viscous 
or liquid
5)	Above 40 °C they should melt without decomposition
6)	Above the mp the viscosity should exhibit a strongly negative 
temperature dependence and the liquid should not tend to stringiness
7)	Waxes should normally melt between ca. 50 and 90 °C (in exceptional 
cases up to 200 °C)
8)	Waxes generally burn with a sooting flame after ignition
9)	Waxes can form pastes or gels and are poor conductors of heat and 
electricity (i.e., they are thermal and electrical insulators).
In the case of higher molar mass polyolefin waxes, differentiating 
between a wax and a thermoplastic polymer is sometimes difficult. This 
differentiation is particularly important for applications where a food 
approval is essential (FDA, EC, MITI in Japan, etc.). In case of doubt, 
relevant national regulations must be consulted.
[4]  DGF-Einheitsmethoden, Abteilung M: Wachse und Wachsprodukte, 
Stuttgart 1975.
Classification
Waxes can be classified according to various criteria such as origin; 
chemical, physical, and engineering properties; or applications (see 
Section 1.2. Definition). The primary differentiation is usually made 
according to origin or occurrence and synthesis. A proposal for a 
classification is shown in Figure (1). Here, waxes are divided into two 
main groups: natural and synthetic. Natural waxes exhibit their wax 
character without chemical treatment, whereas synthetic waxes generally 
acquire their waxy nature in the course of synthesis. There are no 
clear borderlines.
Natural waxes are formed through biochemical processes and are products 
of animal or plant metabolism. Natural waxes formed in earlier 
geological periods are known as fossil waxes. All petroleum, lignite 
(montan wax), and peat waxes belong to this largest category. Fossil 
waxes occur predominantly as minor components of oil, coal, and peat. 
Some deposits with a high wax content were formed by sedimentation. 
Ozocerite separated from oil, and pyropissite, one of the few organic 
minerals, is a mixture of montan wax and resins. Whereas petroleum 
waxes are predominantly nonpolar hydrocarbons, lignite and peat waxes 
consist of oxygen-containing compounds.
Biological wax synthesis is still taking place in nature. Many plants, 
particularly carnaúba palm, and animals — most importantly insects, 
such as bees — produce waxes. These are known as nonfossil or recent 
natural waxes. Natural waxes are seldom used industrially in their 
original form. They are generally converted into modified natural waxes 
by refining, e.g., by distillation, or extraction. Chemical processes, 
such as hydrogenation, bleaching, and oxidation, can also be used. 
Physical and chemical treatment can be combined; the objective of all 
these processes is to obtain a wax that is as pure as possible.
Partially Synthetic Waxes. If natural waxes or waxlike materials are 
modified by chemical reactions such as esterification, amidation, or 
neutralization of acidic waxes (with aqueous alkali or alkaline-earth 
metal hydroxides), partially synthetic waxes are obtained. These can be 
tailored to particular applications. In esterified waxes the 
relationship to natural waxes is still easily recognizable. For 
example, natural montan waxes, which consist mainly of esters of 
long-chain acids with long-chain alcohols, can be converted into acid 
waxes by cleavage of the esters and oxidation of the alcohols. 
Subsequent reaction with dihydric alcohols gives esters that have 
chemical structures comparable to those of the starting materials. 
Amide waxes do not occur naturally to any significant extent. This 
group consists of reaction products of fatty acids with ammonia, 
amines, and diamines. An industrially important amide wax is distearoyl 
ethylenediamine.
Alcohol waxes (lanette waxes) also belong to the partially synthetic 
waxes. They are mixtures of long-chain alcohols that are optimized for 
their main area of use, in ointments and creams for pharmaceuticals and 
cosmetics, by the addition of fatty acid esters and emulsifiers. 
Alcohol waxes can also be used for industrial emulsions with good 
long-term stability.
Wool wax (lanolin) is obtained in crude form from sheep's wool. It is 
refined by chemical and adsorptive bleaching, and sometimes by 
subsequent hydrogenation or separation of the acidic fractions after 
hydrolysis. Wool wax is a mixture of esters, some being derived from 
branched or cyclic waxy or fatty acids and alcohols.
Fully synthetic waxes were developed only in the 20th century. Low 
molar mass compounds are used as starting materials. The products can 
be waxes in the narrower sense of the definition (see Section 1.2. 
Definition), or substances with only partial wax character. The two 
main groups of fully synthetic waxes are the Fischer – Tropsch and the 
polyolefin waxes. These waxes can be classified according to the 
starting material used for production (C1 or C2 chemistry).
C1 Building Blocks. The Fischer – Tropsch (FT) synthesis is described 
elsewhere in detail (® Coal Liquefaction - 2.2. Fischer – Tropsch 
Synthesis). The oldest FT variant is the ARGE process 
(Arbeitsgemeinschaft Ruhrchemie – Lurgi). Synthesis gas is obtained by 
reaction of steam with carbon (® Gas Production - 4. Gas Production 
from Coal, Wood, and Other Solid Feedstocks) and is then converted 
catalytically into a broad spectrum of saturated and unsaturated 
hydrocarbons. Among these products are the Fischer – Tropsch waxes. 
They are characterized by low branching of the hydrocarbon chain and a 
narrow molar mass distribution. They are relatively hard products. The 
ARGE process has been used commercially by SASOL in the Republic of 
South Africa.
Besides carbon, natural gas can also be used as a raw material for C1 
syntheses. The Shell Middle Distillate Synthesis (SMDS) process 
utilizes synthesis gas produced by steam reforming of natural gas [6]. 
Fischer – Tropsch wax fractions are produced and marketed at the new 
SMDS plant in Bintulu (Sarawak/Malaysia). This process is a variant of 
the classical FT process and employs specially developed catalysts.
Polyolefin waxes are, in most cases, products of C2 or C3 chemistry. 
Low molar mass a-olefins, usually ethylene, are polymerized. The other 
route to polyethylene waxes — thermomechanical degradation of 
polyethylene plastic — is now of minor importance. The two most 
important production processes are the high-pressure and the Ziegler 
processes. Recently, polyolefin waxes have also been synthesized by 
using modern metallocene catalysts.
Polyolefin waxes can be homopolymers or copolymers of C2 , C3 , C4 
(ethylene, propene, and butene), or higher a-olefins. Polypropylene 
(PP) waxes are produced by the Ziegler process or by thermomechanical 
degradation of polypropylene plastic. Polypropylene waxes are generally 
partially crystalline. In addition, predominantly amorphous and atactic 
low molar mass polypropylene (APO or APAO) with a waxlike character is 
now produced and marketed by several companies. Besides this deliberate 
production, atactic PP (APP) is still produced as a byproduct of PP 
plastics.
All FT and polyolefin waxes are nonpolar. Polar waxes are obtained by 
subsequent reactions, such as oxidation by air or grafting (e.g., with 
maleic anhydride), optionally followed by neutralization to metallic 
soaps, esterification, or amide formation. Polar polyolefin waxes are 
also accessible via direct copolymerization or addition reactions 
(e.g., of olefins with unsaturated carboxylic acids or esters).
A considerable proportion of industrially processed waxes is used not 
in pure form but as wax compounds. For example, the viscosity and mp of 
paraffin waxes can be increased to the desired degree by mixing with 
polyolefin waxes.
[6]  J. Haggin: "Asian Natural Gas Pipeline Proposed for Easing Energy 
Feedstocks Strains," Chem. Eng. News(1994) no. 6, 17 – 18.
-- 
revenge

 relevant national regulations must be consulted.
Per quanto rigurda la saponificazione intesa come reazione chimica si
puo' fare. Come mi pare di capire dal testo tra i prodotti ottenuti ci
sono unguenti, balsami etc.

Ciao 
Andrea Zille

stracut
Esatto come dici tu, hai capito benissimo, volevo solo informarmi per 
dare una risposta coerente.
reve
-- 
revenge

Ok ragazzi, molte grazie per il chiarimento.
Scusate se riporto la discussione ad un livello
piu' pratico, ma, stabilito quindi che le cere
saponificano ma molto piu' lentamente dei grassi,
come e' possibile eliminarle velocemente da un
bagno acquoso mentre i grassi vengono eliminati
per saponificazione? :)
Grazie per l'attenzione 


Stai confondendo  concetti:
Saponificare significa idrolizzare un composto (trigliceride
normalmente) in una soluzione alcalina.
La funzione dei saponi (sali di acidi carbossilici a lunga catena) e'
quella di formare micelle nelle quali la parte idrofobica idrocarbonica
e' all'interno e la parte idrofila carbossilica del sale dell'acido
grasso e' esposta all'acqua. Il sapone rimuove il grasso dall'acqua
perche' le molecole di grasso sono incamerate nella parte idrofobica
delle micelle e quindi facilmente rimosse in soluzione. Il problema con
le cere e' di non essere neanche un po' solubili in acqua e quindi non
si possono formare micelle.
Ciao
Andrea Zille

 per saponificazione? :)
beh, diciamo che intanto le cere, almeno quelle di cui sopra, 
sono del tutto idroinsolubili, persino più dei grassi stessi, 
per cui dovrebbe quasi bastare raffreddare il bagno poco sotto 
il punto di solidificazione e magari agitare  con un ferramino 
per agglutinarle in blocchi "cerosi" (di sicuro gran parte si 
attacca alle pareti del recipiente e richiede di decantare la 
soluzione, diciamo attraverso un filtro adatto). Un filtro 
"adatto" potrebbe essere carta pre-umidificata o cotone idrofilo 
preumettato con acqua, in modo da limitare un po' l'effetto 
tappo della cera .... se opti per la filtrazione, conviene 
raffreddare nettamente e rendere la cera dura e non solo 
pastosa). LA gran parte dei saponi dovrebbe rimanere invece in 
soluzione, quantomeno in soluzione micellare.
Alternativa, apparentemente veloce ma non esente da rischi, è 
l'estrazione con solventi apolari.
In questo caso si possono tentare solventi completamente 
idrofobi e più restii possibile ad essere emulsionati (ad es. in 
quanto molto densi o molto leggeri, tipo idrocarburi saturi come 
pentano ed esano o carbonio tetracloruro). Anche con questa 
cautela, più che un vero sbattimento in imbuto potrebbe essere 
meglio agitare a lungo magneticamente tentando (imho in parte 
vanamente) di limitare schiuma e formazione di emulsioni. 
Bisogna infatti tenere conto che estrarre soluzioni di 
tensioattivi è fonte di notevoli dispiaceri come tempi di 
manipolazione. Il tetracloruro è discretamente volenteroso nello 
smontare le emulsioni, ma molto dipende da quanto fini sono le 
goccioline.
Certo, l'ideale sarebbe avere un estrattore continuo "dropplet", 
che difficilmente emulsiona alcunché perché produce un flusso 
regolare di gocciolone piuttosto grosse e che precipitano e si 
saldano facilmente, ma la cosa forse è esagerata per le necessità.
Ad ogni modo, l'estrazione rimuove le cere apolari in modo molto 
efficace e completo. Solitamente i solventi di media polarità 
(tipo metilene cloruro, un suicidio nel caso attuale) possono 
estrarre persino un po' di saponi, ma tanto tu li vuoi togliere 
di mezzo per cui la cosa non ti interessa.
ciao
Soviet_Mario
