Accordingly, after uncombined water has been removed, the still contents are in the form of a clear or, at worst, slightly turbid liquid consisting of moderately low molecular weight formaldehyde polymers. (YkP %$+=lV|zSF!D O-K.{'1 o%/=RDt~%_e3KI|3v\&,] 4h6'Dy0RGdzPU}-)q%u8\ The use of such large amounts of-methanol as an inhibitor is a distinct eco nomic waste and represents an appreciable item in the a 1,"? Such aqueous solutions may be employed, if desired, in the preparation of phenolic resins (for example) by standard procedures or, due to the ready solubility of the .paraformaldehyde of my invention in phenols, these resins may be prepared in the essential absence of water thereby achieving a higher productive capacity from a given resin producing installation. 8. That this is not true is shown by the fact that practically all formaldehyde is produced, sold and used in the form of formalin. MN -n M cost of the so inhibited formalin. These additional reagents must be considered as they may yield unwanted effects. Depolymerization also occurs at temperatures below 90 C. but, as would be expected, the time required for depolymerization increases as the depolymerization temperature is decreased. The stability of. 13, 1954 FOREIGN PATENTS 420,993 Great Britain Dec. 12, 1934. Paraformaldehyde, when dissolved in water, breaks down into formaldehyde. This accounts for the large loss of formaldehyde when an aqueous solution of formaldehyde is boiled at atmospheric pressure and also for the greater chemical instability of formalin at elevated storage temperatures (e. g. greater tendency to oxidize to for-micacid,'greater tenden oy to undergo the Cannizzaro reaction under-acidic conditions, et cetera). If, on the other hand, on reaching a temperature of 75- 85 C. the still contents are clear or, at worst, slightly turbid, they are poured onto a glass tray and allowed to cool and solidify. ZM.ZNov/hn!CNr83$`~ {* Ah c"v~7|#7aZ :""`O?S^%> OG8!*CFloN@knI S~$ K>"QB~{^}R!CpQ7~0ai/ C!}E0InTbIM zH`iZS|5NOoVJN4>P6auT1 fD-\F5I{""#"|EFlfmUZ:RU` )')O$f!!ATj9kA$s))^2"a`! Formalin is not'suitable for use in certain formaldehyde condensation reactions, fol-example, the formolit reaction involving'the condensationofformaldehyde and aromatichydrocarbons. However, many vendors use a small amount of methanol or other chemicals to prevent polymerization of formaldehyde in the solution. In addition, the low concentration offormaldehyde in formalin frequently results in a low reaction rate in synthetic processes employing this material as a reactant. When an aqueous solution of formaldehyde is heated to its boiling point under atmospheric pressure a large portion of the formaldehyde is lost with the vapors and comparatively little paraformaldehyde is obtained from the still bottoms. It is important to note, that formaldehyde-based fixation is too slow and may take from a few hours to days to fix samples. However, only formaldehyde (not methylene glycol) have cross-linking ability. Check the pH and adjust with HCl and NaOH if required. The process of producing paraformaldehyde comprising heating to the atmospheric pressure boiling point thereof an aqueous solution containing hydrated formaldehyde and formaldehyde polymers, maintaining said solution at its atmospheric pressure boiling point for a period of about one half to one hour, removing water from the resulting depolymerized solution by evaporation ata pressure in the approximate range 10 to '30 mm. At high temperatures the acidity of the solution increases, due probably to the enhanced rate of oxidation of formaldehyde to formic acid. x]@Vj *v:jsBq2DwE3_ .4Fzlv8g~ofk{Oo~taf=}kvk:x3f6/_Yc[OS|O G?Mn;yfAs@]M7wa 5_HwC|dHAA(hh umToU7@D,73yx:;?355?~AF97ei] D9>`{.hhg|+8-@zoPUq&Od%mMR;.W 50ZTZ%R(N5P*U\ Add 40 g of Paraformaldehyde powder to 1X PBS. In addition,'due to the low concentration of formaldehyde in formalin the rates of reaction in syntheses employing formalin are frequently quite low and thesize of .a batch that can be processed in a given piece of equipment is small. before the still bottoms-exhibit more than a slight turbidity and cooling the still bottoms to produce solid paraformaldehyde. This solution differs from commercially available form (formalin) being relatively pure (devoid of methanol). In immunohistochemistry (IHC) and cell biology experiments, researchers prefer working with PFA solution rather formalin due to the same reason. Finally, most formaldehyde reactions of commercial importance are condensations involving the elimination of water. ScienceDirect is a registered trademark of Elsevier B.V. ScienceDirect is a registered trademark of Elsevier B.V. Microbial Metagenomics, Metatranscriptomics, and Metaproteomics, Sample fixation is commonly thought to be necessary for preservation of cell structure and to facilitate probe hybridization. Commercially it is usual practice to conduct the evaporation in a specially designed kneader which is expensive to construct and operate-and has a low capacity. 9. High temperature storage is equally undesirable.' This evaporation is carried out under reduced pressure in order .to avoid excessive loss of formaldehyde in the evolved vapors. Paraformaldehyde is a polymer of formaldehyde with a wide range of monomeric units typically 8-100. PyS9Fi3,Va "\!FD fu3^9c]Cc/zbT^5bW]t d5xU8Ek 1E;ectc8wH|pc$}]aP gEZxB|P7~'yI If an aqueous solution of formaldehyde is necessary (for example, in the preparation of pentaerythritol) such a solution is readily and quickly prepared from the paraformaldehyde of my invention. Other objects of my inventionwill become apparent as the description'thereof proceeds. Carver College of Medicine `>a7x0"u{Ir"uD=r" !:a%? Production of anhydrous reaction products of phenol and formaldehyde. 6. 431 Newton Road SEjPVT7ub:;_ 8: r^MQOVkHLX dBhOID\@9e-( These last named disadvantages are only very partially overcome by-useof powdered paraformaldehyde but'this product commands a premium of some 3.5 cents per pound over the flake material. 7. Although the gemdicl configuration is very rare in organic chemistry, the additive power of the carbonyl group of formaldehyde is so great that the formation of a formaldehyde hydrate or even a methylene diol would not be too surprising. Paraformaldehyde prepared in accordance with my in vention can be shipped and stored in standard multi-wall. Cool the solution to room temperature and filter to remove particles. Since formalin contains over 60% by weight of water it is necessary to transport, handle and store this large amount of solvent. Many theories have been put forward to explain-the relative non-reactivity of formalin. The process of producing paraformaldehyde comprisingheating to a temperature within the approximate range 9095 C. an aqueoussolution containing hydrated formaldehyde and formaldehyde polymers, maintaining said solution at said temperature for a period of about one half to one hour, removing Water from the resulting depolymerized solution by evaporation at a pressure in the approximate range .10 to 30 mm. The process of producing paraformaldehyde comprising heating to the atmospheric pressure boiling point thereof an aqueous: solution containing hydrated formaldehyde and formaldehyde polymers, maintaining said solution at its atmosphericpressureboiling point for a period of about one half to one hour,.removing Water from the resulting depolymerized solution by evaporation at reducel pressure at such a ratethat the still hot toms reach a temperature. , Yield: 148 parts After this depolymerizing step, vacuum was gradually 1: duced to mm. The final'product from such a-processing procedure is an insoluble and relatively unreactive paraformaldehyde far different in physical and chemical properties from the soluble and relatively'reactive polymers contained in formalin solutions. Paraformaldehyde prepared in accordance with my invention is an eminently suitable source of formaldehyde for use in condensations of this type.

It should be noted that these requirements with respect to materials of construction are necessary not only to prevent corrosion of equipment but also to avoid contamination of the formalin with the products of corrosion. 10% formalin is equivalent to 4% formaldehyde. Also, if desired, the depolymerization may be accomplished with extreme rapidity by heating aqueous formaldehyde solutions under pressure to a temperature above the atmospheric pressure boiling point of the solutions. Fortunately, formaldehyde is very soluble in water and an aqueous solution containing 37% formaldehyde by weight (formalin) is the form in which this aldehydemost frequently appears in commerce. Accessibility These still bottoms are discharged to a convenient container, for example a pan, wherein cooling "and some additional .polymerizationsoon results in solidification of the mass. These may be either hydrates of low molecular weight true polymers or a polyoxymethyl-ene alpha omega diol of low molecular weight. Too much ammonia prevents silver impregnation and too little can cause impregnation of normal tissue, Sodium thiosulfate: 250 ml of a 1.0% (w/v) solution, Potassium ferricyanide: 250 ml of a 0.5% (w/v) solution, Sodium hydroxide: 250 ml of a 0.4% (w/v) solution, Citric acid: 250 ml of a 1.0% (w/v) solution, Formalin (10%, v/v): Add 2 ml 37% commercial formaldehyde solution to 18 ml doubly distilled H2O. Hotplate magnetic stirrer and a magnetic bead. PFA is recommended to be made in 1X PBS buffer (neutral buffered formalin; NBA). z8T ,HU"=g9`SxV::LSnX{PYIFMW4*lXQ[Fmk^a/Y94T*Lxez_WeW$sqp)bc)XtpF+9Zlu2iQ-d\4:Hd#hT\4:D6(Zy>z1.P]3.8g>.b7!V b,p:eK.$"3.>+yw7n In actual practice, my new and novel process fwould usually be employed in connection with aqueous 'solutions of formaldehyde soon after they have been produced.

A temperature of 90-95 C. is preferably used for at this temperature loss of formaldehyde from the solution is not appreciable while the depolymerization reactionproceeds rapidly. 2. Below, we have provided a step by step process to prepare 4% PFA solution. \*AFb 3. It can be stored at ordinary temperatures for any desired period in such packages without adversely affecting solubility or reactivity. The evaporation temperature corresponding to this pressure is suflicient to permit rapid polymerization of formaldehyde. Heating the PFA powder in the solution leads to its depolymerisation. Recovery of formaldehyde as solid polymer, 91%. x\Ks%UR3#7KrQUAD;.^,1 %+&~64_cZTZ&iN}T+_ctl7J[ssz8ibiN>5O_`Jo*vZ#?zNJ|$0dK33c v7L.dM$KJpJ|tO!CH/T1 The resulting solid, which is free from paraformalde hyde molecules of extremely high molecular weight, is readily soluble and highly reactive. by weight; formaldehyde assay,'9l%. O-el5j:_;.x C/|}O"E:mV(4%LT]Ak ;"6"1IqbQP*- JN-n* 7(e1Zl&v hD,goR"upl",~,0| [s=eU+ c_Q-7 of mercury. tf combined water is evaporated under reduced pressure formaldehyde at reduced pressure produces a liquid still bottoms which is clear or only very slightly turbid and is readily discharged from the still to suitable con tainers in which the bottoms rapidly solidify to form readily soluble and highly reactive paraformaldehyde. Hvep[Do Formaldehyde is a gas (B. P. -2l C. which l ven at the boiling point slowly changes to the cyclic jtrimer, trioxymethylene, the rate of this polymerization reaction increasing rapidly with increasing temperature. of mercury, the rate of heat input to the still being so regulated that at least two hours are required for the temperature of the still contents to reach 75-85 C. If at or prior to this point the still contents contain appreciable solid material the depolymerization treatment was inadequate. -It might be thought that the production of paraformaldehyde by the evaporation of'aqueous formaldehyde solutions at reduced pressuresrepresents'a simple solution of all the difliculties entailed in the transportation, handling, storage and use of formalin. Store refrigerated up to 3 months, Sodium phosphate-buffered saline (0.01 M, working solution): Combine 40 ml concentrated sodium phosphate buffer stock, 8.5 g NaCl, and 960 ml doubly distilled H2O. The polymers immediately begin to react with each other to form polymers of higher molecular weight and when only a comparatively small proportion of the uncombined water has been removed this reaction has proceeded to such an extent that the concentration of relatively insoluble, high molecular Weight polymers is suflicient to gel the mixture and make it unmanageable unless highly specialized and expensive equipment is used. The process of producing paraformaldehyde comprising heating to the atmospheric boilingpoint thereof an aqueous solution containing hydrated formaldehyde and formaldehyde polymers, maintaining said solution at its atmospheric pressure boiling point for a period of about one half to one hour, removing water from the resulting deploymerized solution by evaporation at a pressure below 0.1 atmosphere at such a rate that the still bottoms reach a temperature in the range 75-85 C. before the still bottoms. Ammonia may lose its potency over time, so the precise amount required may vary. The production of paraformaldehyde involves so many difficulties that the price of flake paraformaldehyde delivered to major consuming centers issomeWha-t greater than that offormalin on the basis of equal weights of formaldehyde. Traces of many metal salts, for example, iron salts, greatly reduce the stability of formalin. | ":Incontrast, in my new and novel process, the first step involves depolymerization of the polymers present Then the unflfrom a solution which initially consists of monomeric "formaldehyde which, as previously explained, is probably present largely in the form of formaldehyde hydrate or methylene dioL- All free water may be removed before polymerization of the monomeric formaldehyde has proceeded to such an extent as to form insoluble polymers. 48 Eckstein Medical Research Building % Store at room temperature 13 months. Uncombined water was applied to the solution, the pressure finally being reremoved from the solution at this reduced pressure, the evaporation being continued until 'the temperature of the liquid in the still reached75-85"; C. Vacuum was then released and the clear to very slightly turbid still contents were discharged to a shallow pan and were allowed to solidify. If desired, the rate of depolymerization may be somewhat accelerated by boiling the solution under reflux. Nondiscrimination Statement THE PROCESS OF PRODUCING PARAFORMALDEHYDE COMPRISING HEATING TO A TEMPERATURE WITHIN THE APPROXIMATE RANGE 90-100* C. AN AQUEOUS SOLUTION CONTAINING HYDRATED FORMALDEHYDE AND FORMALDEHYDE POLYMERS, MAINTAINING SAID SOLUTION AT SAID TEMPERATURE FOR A PERIOD OF ABOUT ONE HALF TO ONE HOUR, REMOVING WATER FROM THE RESULTING DEPOLYMERIZED SOLUTION BY EVAPORATION AT REDUCED PRESSURE AT SUCH A RATE THAT THE STILL BOTTOMS REACH A TEMPERATURE IN THE RANGE 75-85* C. BEFORE THE STILL BOTTOMS EXHIBIT MORE THAN A SLIGHT TURBIDITY AND COOLING THE STILL BOTTOMS TO PRODUCE SOLID PARAFORMALDEHYDE. [T@8hTeedx3aH#hvRYOm'n`EDib (6WJipH;xk*w~>VO9( GZP?Jpc dCvXS3`zW2^Y1VP AAC%l` f4&7LypSkvtje#'S$Y!0%Pc&p1!.J::_P26yo2-Cg0a[6[ .6u>T:U[j 3"8 o4-=\s"igp&E,"7)~HqZ:~'rBzOQ:|8(|!j0daP+M?i,Q='Y(vKwB>^B[I"\Qr6 F&%$JJ6 << /Length 4 0 R /Filter /FlateDecode >> Be it remembered, that While this invention has been described in connection With specific'details and a specific example thereof, these are illustrative only and are not to be considered limitations on the spirit or scope of said invention except in so far as-these may be incorporated in the appended claims. The solution is corrosive and is not too stable in storage, especially at temperatures 'above and below ordinary roomtemperatures. Add 0.5% Triton X-100 (percentage of Triton X-100 varies between 0.01 to 0.5). The process ofaproducing paraformaldehyde comprising heating to a temperature within the approximate range 90-100" C. an aqueous solution containing hydrated'formaldehy'de and formaldehyde polymers,. l. The process of producing paraformaldehyde comprising heating to a temperature within the approximate range 90-100 C. an aqueous solution containing hydrated formaldehyde and formaldehyde polymers, maintaining said solution at'said temperature for a period .of about one half to one hour, removing water from the resulting depolymerized solution by evaporation at reduced pressure at such a rate that the still'bottoms reach a temperature in the range 75.85 C. before the still bottoms exhibitmore than a slight turbidity and cooling the still bottoms to produce solidparaformaldehyde. Formaldehyde fixes (halts) metabolism by cross-linking protein molecules especially with lysine. When dissolved, paraformaldehyde breaks into formaldehyde in solution. All Rights Reserved During the concentration of an aqueous solution of formaldehyde 'at reduced pressures a point is reachedpq usually at a form-aldehyde content of 5060%, atwhicho separation of insoluble polymers causes the'solution'tof gel. Formalin is quite unstable. Neutral pH prevents the formation of formic acid, which is known to form "formalin pigments" in tissue and slower fixation rates. 4 0 obj stream The adequacy of a given depolymerization treatment may be readily determined by taking an aliquot of the so treated liquid, for example, about one pint, and subjecting it to distillation at a pressure of say 20 mm. _~ay^EhWj6?0Bx3Qv*:yl",#(k6!2RO[iW#>f)0vlCwzRLs%qKUU@*E5$(`n{w^@3u>Q5'#/)c Store PFA solution at room temperature, for 1-2 weeks or at 4oC for a few weeks. At the point of consumption, handling of the solution should be through chemical rubber hose or corrosion resistant pipe to storage fa: T cilities constructed of stainless steel (type 304 or, preferably, types 316 or 317), aluminum (types 25, 38, 528. or 61S-T) or mild steel coated with a suitable resin. H2O and bring to 1000 ml with doubly distilled H2O. Phone: 1-319-335-8103, Copyright 2022 The University of Iowa. Paraformaldehyde prepared in accordance with my invention may be employed in all applications where formalin is customarily employed. zH8y%$!Z7mX,.k ,},O,(D!A{TgjSQCUY Oc*u|De_XNBm}X{^Y1@DR(:9[^'n==vEE;)!OdZ++ i>i$yQ$)(1(TPl' T=$35D%'Nbwp@cDr]=p6E ]nn'< )lqEiG2>}o}*85[]?Cx^riJRe 27obWF@7{,#cN By continuing you agree to the use of cookies. Preferably, I employ a pressure in the approximate range 10 to 30 mm. lest the resin lining be injured. The time required for the depolymerization step depends upon the age of the formaldehyde solution being proc'essed. To offset the corrosivenature of formalin, this material is usually shipped in insulated resin lined tank cars or in resin lined drums. I. University of Iowa Indigenous Land Acknowledgement, University of Iowa Indigenous Land Acknowledgement, Continue heating and stirring until paraformaldehyde is dissolved. 260-615) V p This invention relates principally to a new and novel process for the 1 production of paraformaldehyde. "oNvM[}}>]=*YyTS Paraformaldehyde (PFA) in PBS is one of the widely used fixatives for Immuno-histochemistry (IHC) and fluorescent protein labelled samples. Obviously, these requirements add greatly to the cost of transporting, handling and storing formalin. << /Length 5 0 R /Filter /FlateDecode >>

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