Commentary for Kiddushin 111:10

Second tithe money should not be used to buy food outside of Jerusalem. According to the first opinion, if one uses second tithe money to buy an animal outside of Jerusalem, if unwittingly, the sale is void. The money returns to its “place” meaning it stays second tithe. But if he does so deliberately, the sale is valid and the animal must be brought to Jerusalem and eaten there.
R. Yehudah explains the first opinion—the person was buying an animal to be used as a peace-offering, which seems to have been a normal thing to be done with second tithe money. If he does so intentionally, then the acquisition is valid. But if he was trying to buy a non-sacred animal, meaning his intent was to turn the second tithe into non-sacred money, then the exchange is invalid whether done unwittingly or deliberately.

In the mishnah R. Yehudah said that if one intentionally uses second tithe money to betroth a woman, the betrothal is valid. This contradicts what we just said—if he uses the money deliberately, the sale is not valid.

R. Elazar explains that in the mishnah a woman knows that the second tithe money stays holy and that she must take it to Jerusalem. Therefore, there is no reason for the kiddushin not to be valid. In contrast, when one tries to desacralize second tithe money, the act is invalid and the money remains second tithe.

People should know, according to R. Yirmiyah, that if one buys items that cannot be eaten the money is not desacralized. Second tithe money should be used to buy food to be eaten in Jerusalem. Nevertheless, if one does use second tithe money to buy these things, the sale is valid. He then takes other coins and states that they become second tithe in place of the coins that are in the hand of the seller. Then he brings these coins to Jerusalem and consumes them there (essentially he is penalized by having to spend twice as much). So why is this not the rule with kiddushin? Why don’t we make the man who betrothed the woman redeem the coins and bring them to Jerusalem? Why make the woman bring them?

The woman in the mishnah knows that second tithe remains holy and therefore she will bring the coins the man gave her to Jerusalem. But in a regular case, of a woman who does not know that second tithe must be brought to Jerusalem, the man who betrothed her must himself redeem the coins he gave her and bring them to Jerusalem.

The mishnah we just saw says that if one buys things that cannot be eaten, he redeems those coins, brings the equivalent value in their place, and uses those coins to buy food in Jerusalem.
But R. Yehudah said that if one intentionally tries to desacralize second tithe coins, the coins remain holy. They “return to their place” and the sale is nullified.
Shmuel says that the mishnah here refers to a case where the seller fled and therefore the coins cannot be returned to him. They cannot “return to their place.” In such a case, he may redeem them and use the new coins to buy food in Jerusalem.

The mishnah we just saw says that if one buys things that cannot be eaten, he redeems those coins, brings the equivalent value in their place, and uses those coins to buy food in Jerusalem.
But R. Yehudah said that if one intentionally tries to desacralize second tithe coins, the coins remain holy. They “return to their place” and the sale is nullified.
Shmuel says that the mishnah here refers to a case where the seller fled and therefore the coins cannot be returned to him. They cannot “return to their place.” In such a case, he may redeem them and use the new coins to buy food in Jerusalem.